— !  { 

MKH  • 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


THE 


COMPLETE   WORKS 


COUNT    RUMFORD. 


PUBLISHED    BY   THE    AMERICAN    ACADEMY    OF 
ARTS    AND    SCIENCES. 


VOL.    II. 


BOSTON. 

1873- 


UNIVERSITY  PRESS  :  WELCH,  BICELOW,  &  Co., 
CAMBRIDGE. 


. 


CONTENTS. 


PAGE 

AN  INQUIRY  CONCERNING  THE  WEIGHT  ASCRIBED  TO  HEAT     .         i 

[Read  before  the  Royal  Society,  May  2,  1799.] 

AN  INQUIRY  CONCERNING  THE  NATURE  OF  HEAT  AND  THE 
MODE  OF  ITS  COMMUNICATION 23 

[Read  before  the  Royal  Society,  February  2,  1804.] 

EXPERIMENTAL  INVESTIGATIONS  CONCERNING  HEAT        .        .131 

[Read   before  the  National  Institute  of  France,  April  9  and  30,  and 
May  7,  1804,  and  April  2,  1805.] 

REFLECTIONS  ON  HEAT 166 

[Read  before  the  National  Institute  of  France,  June  26,  1804.] 

HISTORICAL  REVIEW  OF  THE  VARIOUS  EXPERIMENTS  OF  THE 
AUTHOR  ON  THE  SUBJECT  OF  HEAT 188 

EXPERIMENTS  AND  OBSERVATIONS  ON  THE  COOLING  OF  LIQ- 
UIDS IN  VESSELS  OF  PORCELAIN,  GILDED  AND  NOT  GILDED  .  241 

[Read  before  the  National  Institute  of  France,  August  10,  1807.] 

AN  ACCOUNT  OF  A  CURIOUS  PHENOMENON  OBSERVED  ON  THE 
GLACIERS  OF  CHAMOUNY  :  TOGETHER  WITH  SOME  OCCA- 
SIONAL OBSERVATIONS  CONCERNING  THE  PROPAGATION  OF 
HEAT  IN  FLUIDS ,.  .  251 

[Read  before  the  Royal  Society,  December  15,  1803.] 

AN  ACCOUNT  OF  SOME  NEW  EXPERIMENTS  ON  THE  TEMPERA- 
TURE OF  WATER  AT  ITS  MAXIMUM  DENSITY  .  .  .258 

[Read  before  the  National  Institute  of  France,  July  15,  1805.] 


347888 


iv  Contents. 

INQUIRIES  CONCERNING  THE  MODE  OF  THE  PROPAGATION  OF 
HEAT  IN  LIQUIDS 274 

[Read  before  the  National  Institute  of  France,  June  9,  1 806.] 

EXPERIMENTS  AND  OBSERVATIONS  ON  THE  ADHESION  OF  THE 
PARTICLES  OF  WATER  TO  EACH  OTHER  ....  290 

[Read  before  the  National  Institute  of  France,  June  16,  1806.] 

CONTINUATION  OF  EXPERIMENTS  AND  OBSERVATIONS  ON  THE 
ADHESION  OF  THE  PARTICLES  OF  LIQUIDS  TO  EACH  OTHER  .  300 

[Read  before  the  National  Institute  of  France,  March  9,  1807.] 

OF  THE  SLOW  PROGRESS  OF  THE  SPONTANEOUS  MIXTURE  OF 
LIQUIDS  DISPOSED  TO  UNITE  CHEMICALLY  WITH  EACH  OTHER  318 

[Read  before  the  National  Institute  of  France,  March  29,  1807.] 

OF  THE  USE  OF  STEAM  AS  A  VEHICLE  FOR  TRANSPORTING  HEAT    324 

OBSERVATIONS  RELATIVE  TO  THE  MEANS  OF  INCREASING  THE 
QUANTITIES  OF  HEAT  OBTAINED  IN  THE  COMBUSTION  OF 
FUEL. 345 

DESCRIPTION  OF  A  NEW  BOILER,  CONSTRUCTED  WITH  A  VIEW 
TO  THE  SAVING  OF  FUEL 352 

[Read  before  the  National  Institute  of  France,  October  6,  1806.] 

EXPERIMENT  ON  THE  USE  OF  THE  HEAT  OF  STEAM,  IN  PLACE 
OF  THAT  OF  AN  OPEN  FlRE,  IN  THE  MAKING  OF  SOAP  .  .  359 

[Read  before  the  National  Institute  of  France,  October  20,  1 806.] 

ACCOUNT  OF  SOME  NEW  EXPERIMENTS  ON  WOOD  AND  CHAR- 
COAL   362 

[Read  before  the  National  Institute  of  France,  December  30,  1811.] 

RESEARCHES  UPON  THE  HEAT  DEVELOPED  IN  COMBUSTION  AND 
IN  THE  CONDENSATION  OF  VAPOURS 370 

[Read   before  the  National  Institute   of  France,  February  24,  and  No- 
vember 30,  1812.] 


Contents.  v 

Ox  THE  CAPACITY  FOR  HEAT  OR  CALORIFIC  POWER  OF  VARI- 
OUS LIQUIDS 425 

[Read  before  the  National  Institute  of  France,  1812.] 

INQUIRIES  RELATIVE  TO  THE  STRUCTURE  OF  WOOD,  THE  SPE- 
CIFIC GRAVITY  OF  ITS  SOLID  PARTS,  AND  THE  QUANTITY  OF 
LIQUIDS  AND  ELASTIC  FLUIDS  CONTAINED  IN  IT  UNDER  VA- 
RIOUS CIRCUMSTANCES  ;  THE  QUANTITY  OF  CHARCOAL  TO  BE 
OBTAINED  FROM  IT;  AND  THE  QUANTITY  OF  HEAT  PRODUCED 
BY  ITS  COMBUSTION  .  . 435 

[Read  before  the  National  Institute  of  France,  September  28,  and  Oc- 
tober 5,  1812.] 

OF  CHIMNEY  FIREPLACES  .        .        .        .        .        .     484 

,       [Essay  IV.] 

SUPPLEMENTARY  OBSERVATIONS  CONCERNING  CHIMNEY  FIRE- 
PLACES .  ... 559 

[Essay  XI.] 


AN    INQUIRY 

CONCERNING 

THE    WEIGHT    ASCRIBED    TO    HEAT. 

THE  various  experiments  which  have  hitherto  been 
made  with  a  view  to  determine  the  question,  so 
long  agitated,  relative  to  the  weight  which  has  been 
supposed  to  be  gained,  or  to  be  lost,  by  bodies  upon 
their  being  heated,  are  of  a  nature  so  very  delicate,  and 
are  liable  to  so  many  errors,  not  only  on  account  of  the 
imperfections  of  the  instruments  made  use  of,  but  also 
of  those,  much  more  difficult  to  appreciate,  arising  from 
the  vertical  currents  in  the  atmosphere,  caused  by  the 
hot  or  the  cold  body  which  is  placed  in  the  balance, 
that  it  is  not  at  all  surprising  that  opinions  have  been 
so  much  divided,  relative  to  a  fact  so  very  difficult  to 
ascertain. 

It  is  a  considerable  time  since  I  first  began  to  medi- 
tate upon  this  subject,  and  I  have  made  many  experi- 
ments with  a  view  to  its  investigation  ;  and  in  these 
experiments  I  have  taken  all  those  precautions  to  avoid 
errors  which  a  knowledge  of  the  various  sources  of 
them,  and  an  earnest  desire  to  determine  a  fact  which  I 
conceived  to  be  of  importance  to  be  known,  could  in- 
spire ;  but  though  all  my  researches  tended  to  convince 
me  more  and  more  that  a  body  acquires  no  additional 
weight  upon  being  heated,  or,  rather,  that  heat  has  no 
effect  whatever  upon  the  weights  of  bodies,  I  have  been 


2  An  Inquiry  concerning 

so  sensible  of  the  delicacy  of  the  inquiry,  that  I  was  for 
a  long  time  afraid  to  form  a  decided  opinion  upon  the 
subject. 

Being  much  struck  with  the  experiments  recorded  in 
the  Transactions  of  the  Royal  Society,  Vol.  LXXV., 
made  by  Dr.  Fordyce,  upon  the  weight  said  to  be  ac- 
quired by  water  upon  being  frozen  ;  and  being  possessed 
of  an  excellent  balance,  belonging  to  his  Most  Serene 
Highness  the  Elector  Palatine  Duke  of  Bavaria;  early 
in  the  beginning  of  the  winter  of  the  year  1787, — as 
soon  as  the  cold  was  sufficiently  intense  for  my  pur- 
pose,—  I  set  about  to  repeat  those  experiments,  in 
order  to  convince  myself  whether  the  very  extraordi- 
nary fact  related  might  be  depended  on  ;  and  with  a 
view,  to  removing,  as  far  as  was  in  my  power,  every 
source  of  error  and  deception,  I  proceeded  in  the  fol- 
lowing manner. 

Having  provided  a  number  of  glass  bottles,  of  the 
form  and  size  of  what  in  England  is  called  a  Florence 
flask,  —  blown  as  thin  as  possible,  —  and  of  the  same 
shape  and  dimensions,  I  chose  out  from  amongst  them 
two,  which,  after  using  every  method  I  could  imagine 
of  comparing  them  together,  appeared  to  be  so  much 
alike  as  hardly  to  be  distinguished  from  each  other. 

Into  one  of  these  bottles,  which  I  shall  call  A,  I  put 
4107.86  grains  Troy  of  pure  distilled  water,  which 
filled  it  about  half  full ;  and  into  the  other,  B,  I  put 
an  equal  weight  of  weak  spirit  of  wine ;  and,  sealing 
both  the  bottles  hermetically,  and  washing  them,  and 
wiping  them  perfectly  clean  and  dry  on  the  outside,  I 
suspended  them  to  the  arms  of  the  balance,  and  placed 
the  balance  in  a  large  room,  which  for  some  weeks  had 
been  regularly  heated  every  day  by  a  German  stove, 


the   Weight  ascribed  to  Heat.  3 

and  in  which  the  air  was  kept  up  to  the  temperature 
of  61°  of  Fahrenheit's  thermometer,  with  very  little 
variation.  Having  suffered  the  bottles,  with  their  con- 
tents, to  remain  in  this  situation  till  I  conceived  they 
must  have  acquired  the  temperature  of  the  circum- 
ambient air,  I  wiped  them  afresh,  with  a  very'  clean, 
dry  cambric  handkerchief,  and  brought  them  into  the 
most  exact  equilibrium  possible,  by  attaching  a  small 
piece  of  very  fine  silver  wire  to  the  arm  of  the  bal- 
ance to  which  the  bottle  which  was  the  lightest  was 
suspended. 

Having  suffered  the  apparatus  to  remain  in  this  situa- 
tion about  twelve  hours  longer,  and  finding  no  altera- 
tion in  the  relative  weights  of  the  bottles,  —  they  con- 
tinuing all  this  time  to  be  in  the  most  perfect  equi- 
librium, —  I  now  removed  them  into  a  large  uninhab- 
ited room,  fronting  the  north,  in  which  the  air,  which 
was  very  quiet,  was  at  the  temperature  of  29°  F. ;  the 
air  without  doors  being  at  the  same  time  at  27° ;  and 
going  out  of  the  room,  and  locking  the  door  after  me, 
I  suffered  the  bottles  to  remain  forty-eight  hours,  un- 
disturbed, in  this  cold  situation,  attached  to  the  arms 
of  the  balance  as  before. 

At  the  expiration  of  that  time,  I  entered  the  room, 

—  using  the  utmost  caution  not  to  disturb  the  balance, 

—  when,  to  my  great  surprise,  I  found  that  the  bottle 
A  very  sensibly  preponderated. 

The  water  which  this  bottle  contained  was  com- 
pletely frozen  into  one  solid  body  of  ice ;  but  the 
spirit  of  wine,  in  the  bottle  B,  showed  no  signs  of 
freezing. 

I  now  very  cautiously  restored  the  equilibrium  by 
adding  small  pieces  of  the  very  fine  wire  of  which  gold 


4  An  Inquiry  concerning 

lace  is  made,  to  the  arm  of  the  balance  to  which  the  bottle 
B  was  suspended,  when  I  found  that  the  bottle  A  had 
augmented  its  weight  by  35^  part  of  its  whole  weight 
at  the  beginning  of  the  experiment ;  the  weight  of  the 
bottle  with  its  contents  having  been  4811.23  grains 
Troy  (the  bottle  weighing  703.37  grains,  and  the  water 
4107.86  grains),  and  it  requiring  now  -£$fa  parts  of  a 
grain,  added  to  the  opposite  arm  of  the  balance,  to 
counterbalance  it. 

Having  had  occasion,  just  at  this  time,  to  write  to  my 
friend,  Sir  Charles  Blagden,  upon  another  subject,  I 
added  a  postscript  to  my  letter,  giving  him  a  short 
account  of  this  experiment,  and  telling  him  how  "very 
contrary  to  my  expectation  "  the  result  of  it  had  turned 
out ;  but  I  soon  after  found  that  I  had  been  too  hasty 
in  my  communication.  Sir  Charles,  in  his  answer  to 
my  letter,  expressed  doubts  respecting  the  fact;  but, 
before  his  letter  had  reached  me,  I  had  learned  from  my 
own  experience  how  very  dangerous  it  is  in  philosoph- 
ical investigations  to  draw  conclusions  from  single  ex- 
periments. 

Having  removed  the  balance,  with  the  two  bottles 
attached  to  it,  from  the  cold  into  the  warm  room 
(which  still  remained  at  the  temperature  of  61°),  the  ice 
in  the  bottle  A  gradually  thawed ;  and,  being  at  length 
totally  reduced  to  water,  and  this  water  having  acquired 
the  temperature  of  the  surrounding  air,  the  two  bottles, 
after  being  wiped  perfectly  clean  and  dry,  were  found  to 
weigh  as  at  the  beginning  of  the  experiment,  before  the 
water  was  frozen. 

This  experiment,  being  repeated,  gave  nearly  the  same 
result,  —  the  water  appearing  when  frozen  to  be  heavier 
than  in  its  fluid  state;  but  some  irregularity  in  the 


tfie   Weight  ascribed  to  Heat.  5 

manner  in  which  the  water  lost  the  additional  weight 
which  it  had  appeared  to  acquire  upon  being  frozen 
when  it  was  afterwards  thawed,  as  also  a  sensible  differ- 
ence in  the  quantities  of  weight  apparently  acquired  in 
the  different  experiments,  led  me  to  suspect  that  the 
experiment  could  not  be  depended  on  for  deciding  the 
fact  in  question.  I  therefore  set  about  to  repeat  it, 
with  some  variations  and  improvements  ;  but  before  I 
give  an  account  of  my  further  investigations  relative  to 
this  subject,  it  may  not  be  amiss  to  mention  the  method 
I  pursued  for  discovering  whether  the  appearances  men- 
tioned in  the  foregoing  experiments  might  not  arise 
from  the  imperfections  of  my  balance ;  and  it  may  like- 
wise be  proper  to  give  an  account,  in  this  place,  of  an 
intermediate  experiment  which  I  made,  with  a  view  to 
discover,  by  a  shorter  route,  and  in  a  manner  less  ex- 
ceptionable than  that  above  mentioned,  whether  bodies 
actually  lose  or  acquire  any  weight  upon  acquiring  an 
additional  quantity  of  latent  heat. 

My  suspicions  respecting  the  accuracy  of  the  balance 
arose  from  a  knowledge — which  I  acquired  from  the 
maker  of  it  —  of  the  manner  in  which  it  was  con- 
structed. 

The  three  principal  points  of  the  balance  having  been 
determined,  as  nearly  as  possible,  by  measurement,  the 
axes  of  motion  were  firmly  fixed  in  their  places,  in  a 
right  line,  and,  the  beam  being  afterwards  finished,  and 
its  two  arms  brought  to  be  in  equilibrio,  the  balance 
was  proved,  by  suspending  weights,  which  before  were 
known  to  be  exactly  equal,  to  the  ends  of  its  arms. 

If  with  these  weights  the  balance  remained  in  equi- 
librio, it  was  considered  as  a  proof  that  the  beam  was 
just ;  but  if  one  arm  was  found  to  preponderate,  the 


6  An  Inquiry  concerning 

other  was  gradually  lengthened,  by  beating  it  upon  an 
anvil,  until  the  difference  of  the  lengths  of  the  arms  was 
reduced  to  nothing,  or  until  equal  weights,  suspended 
to  the  two  arms,  remained  in  equilibrio ;  care  being 
taken  before  each  trial  to  bring  the  two  ends  of  the 
beam  to  be  in  equilibrio,  by  reducing  with  a  file  the 
thickness  of  the  arm  which  had  been  lengthened. 

Though  in  this  method  of  constructing  balances  the 
most  perfect  equality  in  the  lengths  of  the  arms  may  be 
obtained,  and  consequently  the  greatest  possible  accu- 
racy, when  used  at  a  time  when  the  temperature  of  the 
air  is  the  same  as  when  the  balance  was  made,  yet,  as  it 
may  happen  that,  in  order  to  bring  the  arms  of  the  bal- 
ance to  be  of  the  same  length,  one  of  them'  may  be 
much  more  hammered  than  the  other,  I  suspected  it 
might  be  possible  that  the  texture  of  the  metal  forming 
the  two  arms  might  be  rendered  so  far  different  by  this 
operation  as  to  occasion  a  difference  in  their  expansions 
with  heat ;  and  that  this  difference  might  occasion  a 
sensible  error  in  the  balance,  when,  being  charged  with 
a  great  weight,  it  should  be  exposed  to  a  considerable 
change  of  temperature. 

To  determine  whether  the  apparent  augmentation  of 
weight,  in  the  experiments  above  related,  arose  in  any 
degree  from  this  cause,  I  had  only  to  repeat  the  experi- 
ment, causing  the  two  bottles  A  and  B  to  change  places 
upon  the  arms'  of  the  balance  ;  but,  as  I  had  already 
found  a  sensible  difference  in  the  results  of  different 
repetitions  of  the  same  experiment,  made  as  nearly  as 
possible  under  the  same  circumstances,  and  as  it  was 
above  all  things  of  importance  to  ascertain  the  accuracy 
of  my  balance,  I  preferred  making  a  particular  experi- 
ment for  that  purpose. 


the   Weight  ascribed  to  Heat.  7 

My  first  idea  was,  to  suspend  to  the  arms  of  the  bal- 
ance, by  very  fine  wires,  two  equal  globes  of  glass,  filled 
with  mercury,  and,  suffering  them  to  remain  in  my 
room  till  they  should  have  acquired  the  known  tempera- 
ture of  the  air  in  it,  to  have  removed  them  afterward 
into  the  cold,  and  to  have  seen  if  they  still  remained  in 
equilibrio  under  such  difference  of  temperature  ;  but, 
considering  the  obstinacy  with  which  moisture  adheres 
to  the  surface  of  glass,  and  being  afraid  that  somehow 
or  other,  notwithstanding  all  my  precautions,  one  of  the 
globes  might  acquire  or  retain  more  of  it  than  the  other, 
and  that  by  that  means  its  apparent  weight  might  be 
increased ;  and  having  found  by  a  former  experiment, 
of  which  an  account  is  given  in  one  of  the  preceding 
papers  (that  on  the  Moisture  absorbed  from  the  Atmos- 
phere by  various  Substances),  that  the  gilt  surfaces  of 
metals  do  not  attract  moisture  (see  Vol.  I.  p.  232), 
instead  of  the  glass  globes  filled  with  mercury,  I  made 
use  of  two  equal  solid  globes  of  brass,  well  gilt  and 
burnished,  which  I  suspended  to  the  arms  of  the  bal- 
ance by  fine  gold  wires. 

These  globes,  which  weighed  4975  grains  each,  being 
wiped  perfectly  clean,  and  having  acquired  the  tempera- 
ture (61°)  of  my  room,  in  which  they  were  exposed 
more  than  twenty-four  hours,  were  brought  into  the 
most  scrupulous  equilibrium,  and  were  then  removed, 
attached  to  the  arms  of  the  balance,  into  a  room  in 
which  the  air  was  at  the  temperature  of  26°,  where  they 
were'  left  all  night. 

The  result  of  this  trial  furnished  the  most  satisfac- 
tory proof  of  the  accuracy  of  the  balance  ;  for,  upon 
entering  the  room,  I  found  the  equilibrium  as  perfect  as 
at  the  beginning  of  the  experiment. 


8  An  Inquiry  concerning 

Having  thus  removed  my  doubts  respecting  the  ac- 
curacy of  my  balance,  I  now  resumed  my  investigations 
relative  to  the  augmentation  of  weight  which  fluids  have 
been  said  to  acquire  upon  being  congealed. 

In  the  experiments  which  I  had  made,  I  had,  as  I 
then  imagined,  guarded  as  much  as  possible  against 
every  source  of  error  and  deception.  The  bottles  being 
of  the  same  size,  neither  any  occasional  alteration  in  the 
pressure  of  the  atmosphere  during  the  experiment,  nor 
the  necessary  and  unavoidable  difference  in  the  densities 
of  the  air  in  the  hot  and  in  the  cold  rooms  in  which 
they  were  weighed,  could  affect  their  apparent  weights ; 
and  their  shapes  and  their  quantities  of  surface  being 
the  same,  and  as  they  remained  for  such  a  considerable 
length  of  time  in  the  heat  and  cold  to  which  they  were 
exposed,  I  flattered  myself  that  the  quantities  of  mois- 
ture remaining  attached  to  their  surfaces  could  not  be 
so  different  as  sensibly  to  affect  the  results  of  the  experi- 
ments. But,  in  regard  to  this  last  circumstance,  I  after- 
wards found  reason  to  conclude  that  my  opinion  was 
erroneous. 

Admitting  the  fact  stated  by  Dr.  Fordyce,  —  and 
which  my  experiments  had  hitherto  rather  tended  to 
corroborate  than  to  contradict,  —  I  could  not  conceive 
any  other  cause  for  the  augmentation  of  the  apparent 
weight  of  water  upon  its  being  frozen  than  the  loss  of 
so  great  a  proportion  of  its  latent  heat  as  that  fluid  is 
known  to  evolve  when  it  congeals ;  and  I  concluded 
that,  if  the  loss  of  latent  heat  added  to  the  weight  of 
one  body,  it  must  of  necessity  produce  the  same  effect 
on  another,  and  consequently,  that  the  augmentation  of 
the  quantity  of  latent  heat  must  in  all  bodies  and  in 
all  cases  diminish  their  apparent  weights. 


the   Weight  ascribed  to  Heat.  9 

To  determine  whether  this  is  actually  the  case  or  not, 
I  made  the  following  experiment. 

Having  provided  two  bottles,  as  nearly  alike  as  pos- 
sible, and  in  all  respects  similar  to  those  made  use  of  in 
the  experiments  above  mentioned,  into  one  of  them  I 
put  4012.46  grains  of  water,  and  into  the  other  an  equal 
weight  of  mercury ;  and,  sealing  them  hermetically,  and 
suspending  them  to  the  arms  of  the  balance,  I  suffered 
them  to  acquire  the  temperature  of  my  room,  61°; 
then,  bringing  them  into  a  perfect  equilibrium  with  each 
other,  I  removed  them  into  a  room  in  which  the  air  was 
at  the  temperature  of  34°,  where  they  remained  twenty- 
four  hours.  But  there  was  not  the  least  appearance  of 
either  of  them  acquiring  or  losing  any  weight. 

Here  it  is  very  certain  that  the  quantity  of  heat  lost 
by  the  water  must  have  been  very  considerably  greater 
than  that  lost  by  the  mercury,  the  specific  quantities 
of  latent  heat  in  water  and  in  mercury  having  been 
determined  to  be  to  each  other  as  1000  to  33  ;  but 
this  difference  in  the  quantities  of  heat  lost  produced 
no  sensible  difference  on  the  weights  of  the  fluids  in 
question. 

Had  any  difference  of  weight  really  existed,  had  it 
been  no  more  than  one  millionth  part  of  the  weight  of 
either  of  the  fluids,  I  should  certainly  have  discovered 
it;  and  had  it  amounted  to  so  much  as  y-jnTVur  Part  °f 
that  weight,  I  should  have  been  able  to  have  measured 
it,  so  sensible  and  so  very  accurate  is  the  balance 
which  I  used  in  these  experiments. 

I  was  now  much  confirmed  in  my  suspicions  that  the 
apparent  augmentation  of  the  weight  of  the  water  upon' 
its  being  frozen,  in  the  experiments  before  related,  arose 
from  some  accidental  cause ;  but  I  was  not  able  to  con- 


io  An  Inquiry  concerning 

ceive  what  that  cause  could  possibly  be,  unless  it  were 
either  a  greater  quantity  of  moisture  attached  to  the 
external  surface  of  the  bottle  which  contained  the  water 
than  to  the  surface  of  that  containing  the  spirits  of 
wine,  or  some  vertical  current  or  currents  of  air  caused 
by  the  bottles,  or  one  of  them  not  being  exactly  of  the 
temperature  of  the  surrounding  atmosphere. 

Though  I  had  foreseen,  and,  as  I  thought,  guarded 
sufficiently  against,  these  accidents,  by  making  use  of 
bottles  of  the  same  size  and  form,  and  which  were  blown 
of  the  same  kind  of  glass  and  at  the  same  time,  and 
by  suffering  the  bottles  in  the  experiments  to  remain 
for  so  considerable  a  length  of  time  exposed  to  the  dif- 
ferent degrees  of  heat  and  of  cold  which  alternately 
they  were  made  to  acquire ;  yet,  as  I  did  not  know  the 
relative  conducting  powers  of  ice  and  of  spirit  of  wine 
with  respect  to  heat,  or,  in  other  words,  the  degrees 
of  facility  or  difficulty  with  which  they  acquire  the  tern- 
perature  of  the  medium  in  which  they  are  exposed, 
or  the  time  taken  up  in  that  operation,  and,  conse- 
quently, was  not  absolutely  certain  as  to  the  equality 
of  the  temperatures  of  the  contents  of  the  bottles  at 
the  time  when  their  weights  were  compared,  I  deter- 
mined now  to  repeat  the  experiments,  with  such  va- 
riations as  should  put  the  matter  in  question  out  of  all 
doubt. 

I  was  the  more  anxious  to  assure  myself  of  the  real 
temperatures  of  the  bottles  and  their  contents,  as  any 
difference  in  their  temperatures  might  vitiate  the  ex- 
periment, not  only  by  causing  unequal  currents  in 
the  air,  but  also  by  causing,  at  the  same  time,  a  greater 
or  less  quantity  of  moisture  to  remain  attached  to  the 
glass. 


the   Weight  ascribed  to  Heat.  n 

To  remedy  these  evils,  and  also  to  render  the  experi- 
ment more  striking  and  satisfactory  in  other  respects,  I 
proceeded  in  the  following  manner :  — 

Having  provided  three  bottles,  A,  B,  and  C,  as 
nearly  alike  as  possible,  and  resembling  in  all  respects 
those  already  described,  into  the  first,  A,  I  put  4214.28 
grains  of  water,  and  a  small  thermometer,  made  on 
purpose  for  the  experiment,  and  suspended  in  the  bot- 
tle in  such  a  manner  that  its  bulb  remained  in  the  mid- 
dle of  the  mass  of  water;  into  the  second  bottle,  B,  I 
put  a  like  weight  of  spirit  of  wine,  with  a  like  thermom- 
eter ;  and,  into  the  bottle  C,  I  put  an  equal  weight  of 
mercury. 

These  bottles,  being  all  hermetically  sealed,  were 
placed  in  a  large  room,  in  a  corner  far  removed  from 
the  doors  and  windows,  and  where  the  air  appeared 
to  be  perfectly  quiet ;  and,  being  suffered  to  remain 
in  this  situation  more  than  twenty-four  hours,  the  heat 
of  the  room  (61°)  being  kept  up  all  that  time  with  as 
little  variation  as  possible,  and  the  contents  of  the  bot- 
tles A  and  B  appearing,  by  their  inclosed  thermometers, 
to  be  exactly  at  the  same  temperature,  the  bottles  were 
all  wiped  with  a  very  clean,  dry,  cambric  handkerchief; 
and,  being  afterwards  suffered  to  remain  exposed  to  the 
free  air  of  the  room  a  couple  of  hours  longer,  in  order 
that  any  inequalities  in  the  quantities  of  heat,  or  of 
the  moisture  attached  to  their  surfaces,  which  might 
have  been  occasioned  by  the  wiping,  might  be  corrected 
by  the  operation  of  the  atmosphere  by  which  they  were 
surrounded,  they  were  all  weighed,  and  were  brought  in- 
to the  most  exact  equilibrium  with  each  other,  by  means 
of  small  pieces  of  very  fine  silver  wire,  attached  to  the 
necks  of  those  of  the  bottles  which  were  the  lightest. 


12  An  Inquiry  concerning 

This  being  done,  the  bottles  were  all  removed  into  a 
room  in  which  the  air  was  at  30°,  where  they  were  suf- 
fered to  remain,  perfectly  at  rest  and  undisturbed,  forty- 
eight  hours ;  the  bottles  A  and  B  being  suspended  to 
the  arms  of  the  balance,  and  the  bottle  C  suspended,  at 
an  equal  height,  to  the  arm  of  a  stand  constructed  for 
that  purpose,  and  placed  as  near  the  balance  as  possible, 
and  a  very  sensible  thermometer  suspended  by  the  side 
of  it. 

At  the  end  of  forty-eight  hours,  during  which  time 
the  apparatus  was  left  in  this  situation,  I  entered  the 
room,  opening  the  door  very  gently  for  fear  of  dis- 
turbing the  balance ;  when  I  had  the  pleasure  to  find 
the  three  thermometers,  viz.  that  in  the  bottle  A,  — 
which  was  now  inclosed  in  a  solid  cake  of  ice,  —  that 
in  the  bottle  B,  and  that  suspended  in  the  open  air 
of  the  room,  all  standing  at  the  same  point,  29°  F., 
and  the  bottles  A  and  B  remaining  in  the  most  perfect 
equilibrium. 

To  assure  myself  that  the  play  of  the  balance  was 
free,  I  now  approached  it  very  gently,  and  caused  it  to 
vibrate ;  and  I  had  the  satisfaction  to  find,  not  only 
that  it  moved  with  the  utmost  freedom,  but  also,  when 
its  vibration  ceased,  that  it  rested  precisely  at  the  point 
from  which  it  had  set  out. 

I  now  removed  the  bottle  B  from  the  balance,  and 
put  the  bottle  C  in  ts  place;  and  I  found  that  that 
likewise  remained  of  the  same  apparent  weight  as  at  the 
beginning  of  the  experiment,  being  in  the  same  per- 
fect equilibrium  with  the  bottle  A  as  at  first. 

I  afterwards  removed  the  whole  apparatus  into  a 
warm  room,  and  causing  the  ice  in  the  bottle  A  to 
thaw,  and  suffering  the  three  bottles  to  remain  till  they 


the   Weight  ascribed  to  Heat.  13 

and  their  contents  had  acquired  the  exact  temperature 
of  the  surrounding  air,  I  wiped  them  very  clean,  and, 
comparing  them  together,  I  found  their  weights  re- 
mained unaltered. 

This  experiment  I  afterwards  repeated  several  times, 
and  always  with  precisely  the  same  result,  —  the  water 
in  no  instance  appearing  to  gain,  or  to  lose,  the  least 
weight  upon  being  frozen  or  upon  being  thawed  ; 
neither  were  the  relative  weights  of  the  fluids  in  either 
of  the  other  bottles  in  the  least  changed  by  the  various 
degrees  of  heat  and  of  cold  to  which  they  were  exposed. 

If  the  bottles  were  weighed  at  a  time  when  their  con- 

O 

tents  were  not  precisely  of  the  same  temperature^  they 
would  frequently  appear  to  have  gained,  or  to  have 
lost,  something  of  their  weights ;  but  this  doubtless 
arose  from  the  vertical  currents  which  they  caused  in 
the  atmosphere,  upon  being  heated  or  cooled  in  it,  or 
to  unequal  quantities  of  moisture  attached  to  the  sur- 
faces of  the  bottles,  or  to  both  these  causes  operating 
together. 

As  I  knew  that  the  conducting  power  of  mercury, 
with  respect  to  heat,  was  considerably  greater  than  either 
that  of  water  or  that  of  spirit  of  wine,  while  its  ca- 
pacity for  receiving  heat  is  much  less  than  that  of  either 
of  them,  I  did  not  think  it  necessary  to  inclose  a  ther- 
mometer in  the  bottle  C,  which  contained  the  mercury ; 
for  it  was  evident  that,  when  the  contents  of  the  other 
two  bottles  should  appear,  by  their  thermometers,  to 
have  arrived  at  the  temperature  of  the  medium  in  which 
they  were  exposed,  the  contents  of  the  bottle  C  could 
not  fail  to  have  acquired  it  also,  and  even  to  have  ar- 
rived at  it  before  them  ;  for  the  time  taken  up  in  the 
heating  or  in  the  cooling  of  any  body,  is,  c<eteris  paribus. 


14  An  Inquiry  concerning 

as  the  capacity  of  the  body  to  receive  and  retain  heat, 
directly,  and  as  its  conducting  power,  inversely. 

The  bottles  were  suspended  to  the  balance  by  silver 
wires  about  two  inches  long,  with  hooks  at  the  ends  of 
them  ;  and,  in  removing  and  changing  the  bottles,  I 
took  care  not  to  touch  the  glass.  I  likewise  avoided 
upon  all  occasions,  and  particularly  in  the  cold  room, 
coming  near  the  balance  with  my  breath,  or  touching  it, 
or  any  part  of  the  apparatus,  with  my  naked  hands. 

Having  determined  that  water  does  not  acquire  or  lose 
any  weight  upon  being  changed  from  a  state  of  fluidity 
to  that  of  ice,  and  vice  versa,  I  shall  now  take  my  final 
leave  of  a  subject  which  has  long  occupied  me,  and 
which  has  cost  me  much  pains  and  trouble ;  being  fully 
convinced,  from  the  results  of  the  above-mentioned  ex- 
periments, that  if  heat  be  in  fact  a  substance,  or  matter, 
—  a  fluid  sui  generis,  as  has  been  supposed,  —  which, 
passing  from  one  body  to  another,  and  being  accumu- 
lated, is  the  immediate  cause  of  the  phenomena  we  ob- 
serve in  heated  bodies, — of  which,  however,  I  cannot 
help  entertaining  doubts,  —  it  must  be  something  so 
infinitely  rare,  even  in  its  most  condensed  state,  as  to 
baffle  all  our  attempts  to  discover  its  gravity.  And  if 
the  opinion  which  has  been  adopted  by  many  of  our 
ablest  philosophers,  that  heat  is  nothing  more  than  an 
intestine  vibratory  motion  of  the  constituent  parts  of 
heated  bodies,  should  be  well  founded,  it  is  clear  that 
the  weights  of  bodies  can  in  no  wise  be  affected  by  such 
motion. 

It  is,  no  doubt,  upon  the  supposition  that  heat  is  a 
substance  distinct  from  the  heated  body,  and  which  is 
accumulated  in  it,  that  all  the  experiments  which  have 
been  undertaken  with  a  view  to  determine  the  weight 


the   Weight  ascribed  to  Heat.  15 

which  bodies  have  been  supposed  to  gain  or  to  lose 
upon  being  heated  or  cooled,  have  been  made ;  and 
upon  this  supposition,  —  but  without,  however,  adopt- 
ing it  entirely,  as  I  do  not  conceive  it  to  be  sufficiently 
proved,  — all  my  researches  have  been  directed. 

The  experiments  with  water  and  with  ice  were  made 
in  a  manner  which  I  take  to  be  perfectly  unexception- 
able, in  which  no  foreign  cause  whatever  could  affect 
the  results  of  them ;  and  the  quantity  of  heat  which 
water  is  known  to  part  with,  upon  being  frozen,  is  so 
considerable,  that  if  this  loss  has  no  effect  upon  its 
apparent  weight,  it  may  be  presumed  that  we  shall 
never  be  able  to  contrive  an  experiment  by  which  we 
can  render  the  weight  of  heat  sensible. 

Water,  upon  being  frozen,  has  been  found  to  lose  a 
quantity  of  heat  amounting  to  140  degrees  of  Fahren- 
heit's thermometer  ;  or  —  which  is  the  same  thing —  the 
heat  which  a  given  quantity  of  water,  previously  cooled 
to  the  temperature  of  freezing,  actually  loses  upon 
being  changed  to  ice,  if  it  were  to  be  imbibed  and 
retained  by  an  equal  quantity  of  water,  at  the  given 
temperature  (that  of  freezing),  would  heat  it  140  de- 
grees, or  would  raise  it  to  the  temperature  of  (32°  -J- 
140)  172°  of  Fahrenheit's  thermometer,  which  is  only 
40°  short  of  that  of  boiling  water ;  consequently,  any 
given  quantity  of  water,  at  the  temperature  of  freez- 
ing, upon  being  actually  frozen,  loses  almost  as  much 
heat  as,  added  to  it,  would  be  sufficient  to  make  it 
boil. 

It  is  clear,  therefore,  that  the  difference  in  the  quan- 
tities of  heat  contained  by  the  water  in  its  fluid  state 
and  heated  to  the  temperature  of  61°  F.,  and  by  the 
ice,  in  the  experiments  before  mentioned,  was  very 


1 6  An  Inquiry  concerning 

nearly  equal  to  that  between  water  in  a  state  of  boiling, 
and  the  same  at  the  temperature  of  freezing. 

But  this  quantity  of  heat  will  appear  much  more  con- 
siderable when  we  consider  the  great  capacity  of  water 
to  contain  heat,  and  the  great  apparent  effect  which  the 
heat  that  water  loses  upon  being  frozen  would  produce 
were  it  to  be  imbibed  by,  or  communicated  to,  any 
body  whose  power  of  receiving  and  retaining  heat  is 
much  less. 

The  capacity  of  water  to  receive  and  retain  heat  — 
or  what  has  been  called  its  specific  quantity  of  latent 
heat  —  has  been  found  to  be  to  that  of  gold  as  1000 
to  50,  or  as  20  to  i  ;  consequently,  the  heat  which  any 
given  quantity  of  water  loses  upon  being  frozen,  were 
it  to  be  communicated  to  an  equal  weight  of  gold  at 
the  temperature  of  freezing,  the  gold,  instead  of  being 
heated  162  degrees,  would  be  heated  140  X  20  =  2800 
degrees,  or,  would  be  raised  to  a  bright  red  heat. 

It  appears,  therefore,  to  be  clearly  proved  by  my  ex- 
periments, that  a  quantity  of  heat  equal  to  that  which 
4214  grains  (or  about  9!  oz.)  of  gold  would  require  to 
heat  it  from  the  temperature  of  freezing  water  to  be  red 
hot,  has  no  sensible  effect  upon  a  balance  capable  of  indi- 
cating so  small  a  variation  of  weight  as  that  of  J-Q-Q^-Q-Q-Q 
part  of  the  body  in  question;  and,  if  the  weight  of 
gold  is  neither  augmented  nor  lessened  by  one  millionth 
•part,  upon  being  heated  from  the  point  of  freezing  water 
to  that  of  a  bright  red  heat,  I  think  we  may  very  safely 
conclude,  that  ALL  ATTEMPTS  TO  DISCOVER  ANY  EFFECT 

OF  HEAT  UPON  THE  APPARENT  WEIGHTS  OF  BODIES  WILL 
BE  FRUITLESS. 


the  Weight  ascribed  to  Heat.  17 


SU  PPLEMENT. 

THE  foregoing  paper  having  been  originally  drawn 
up  for  the  purpose  of  being  laid  before  the  Royal 
Society,  my  respect  for  that  learned  body  induced  me 
to  confine  my  observations  to  such  ^points  as  I  con- 
ceived to  be  new;  and  I  took  no  notice  whatever  of  a 
considerable  number  of  experiments  which  I  had  made 
in  the  course  of  my  investigations,  because  they  were 
very  similar  to  experiments  that  had  before  been  made 
by  other  persons ;  and  because  their  results  did  not 
appear  to  me  to  afford  sufficient  grounds  to  form  arty 
decisive  opinion  respecting  the  matter  in  question. 
There  were,  however,  among  my  experiments,  two  or 
three  of  which  I  shall  now  give  an  account,  which  will 
probably  be  thought  sufficiently  interesting  to  deserve 
being  mentioned. 

Most  of  the  experiments,  from  the  results  of  which 
philosophers  had  been  induced  to  form  their  opinions 
respecting  the  ponderability  of  heat,  had  been  made  by 
weighing  the  same  given  body  at  different  temperatures. 
Thus,  solid  globes  of  metal  —  cannon-balls,  for  instance 
—  had  frequently  been  weighed  when  cold,  and  then,  be- 
ing heated  red-hot,  had  been  again  weighed  at  that  high 
temperature,  and,  from  the  apparent  difference  of  the 
weight  of  the  ball  when  cold  and  when  red-hot,  conclu- 
sions had  been  formed  respecting  the  weight  or  levity  of 
heat.  But  had  the  numerous  causes  of  error  in  these 
most  difficult  experiments  been  less  evident  than  they 
are,  yet  the  results  of  the  experiments  of  this  kind  which 
have  hitherto  been  made  by  different  persons  have 
.  VOL.  ii.  2 


1 8  An  Inquiry  concerning 

been  so  various  and  contradictory  that  no  reliance 
whatever  can  be  placed  on  them. 

When  a  hot  body  is  suspended  in  the  air  to  the  arm 
of  a  balance  in  order  to  its  being  weighed,  as  it  con- 
tinually gives  off  heat  to  the  fluid  in  contact  with  it, 
this  communication  of  heat  occasions  a  strong  ascend- 
ing current  of  air  to  be  formed  over  and  by  the  sides 
of  the  hot  body,  which  current  cannot  fail  to  affect  the 
result  of  the  experiment,  and  render  the  conclusions 
drawn  from  it  fallacious.  To  prevent,  if  possible,  these 
causes  of  error,  the  following  experiments  were  con- 
trived. 

The  hot  body  to  be  weighed,  which  was  a  small 
metallic  ball,  heated  red-hot,  was  placed  in  the  scale  of 
the  balance  in  a  small  hemispherical  porcelain  cup, 
which  had  a  slender  foot,  or  stand,  about  one  inch 
high  ;  and  this  cup,  with  the  hot  ball  in  it,  was  covered 
over  by  a  porcelain  coffee-cup,  turned  upside  down, 
which,  without  touching  the  hot  ball,  confined  the 
heated  air  which  surrounded  it.  This  coffee-cup  and 
the  porcelain  stand  were  very  exactly  balanced,  by 
weights  in  the  opposite  side,  before  the  ball  was  intro- 
duced. 

The  following  experiment  was  made  at  Munich  on 
the  2oth  of  April,  1785.  The  weather  being  cloudy, 
with  intervals  of  sunshine,  the  thermometer  in  my 
room  stood  at  52°  F.,  and  the  barometer  26  inches  4 
lines,  French  measure. 

At  30  minute*  after  noon,  a  small  bullet,  or  grape- 
shot,  of  cast-iron,  very  well  formed,  and  apparently 
solid,  having  been  well  washed  and  cleaned  by  scouring 
with  sand,  and  thoroughly  dried,  was  exposed  in  a 
clean  vessel  of  porcelain  in  the  midst  of  a  mixture  of 


the   Weight  ascribed  to  Heat.    -  19 

pounded  ice  and  sea  salt,  till  it  had  acquired  the  tem- 
perature of  25°  F.  (7  degrees  below  the  point  of  freez- 
ing water),  when  it  was  carefully  weighed,  and  found 
to  weigh  very  exactly  773  Jf-  grains  Troy. 

At  i  h.  30/72.  P.  M.,  the  same  bullet  having  been  ex- 
posed 30  minutes  in  a  clean,  dry  vessel  of  porcelain, 
placed  in  a  sand  heat,  at  the  temperature  of  212°  F.,  or 
that  of  boiling  water,  was  again  weighed,  while  yet  hot, 
and  found  to  weigh  no  more  than  773^  grains. 

At  2  h.  o  m.  P.  M.,  the  bullet  having  now  been  ex- 
posed 15  minutes,  in  a  clean  new  Hessian  crucible, 
well  covered,  to  the  heat  of  a  strong  charcoal  fire,  and 
being  thoroughly  red-hot,  was  found  to  weigh  773  f£ 
grains. 

The  bullet,  being  yet  red-hot,  was  put  again  into  the 
crucible,  and  being  once  more  exposed  to  the  fire,  which 
now  burned  very  bright,  at  ih.  20  m.  it  had  acquired  a 
white  heat,  and  began  to  show  signs  of  melting,  some 
small  bubbles  appearing  upon  its  surface.  In  this  state 
it  was  taken  from  the  fire,  and  very  carefully  weighed 
sixteen  times  successively,  at  different  intervals,  when 
it  was  found  to  weigh  as  follows :  — 

Time  when  weighed.  Was  found  to  weigh. 


2h. 
2 
2 
1 

20  m.    

21     
23   .     .     .    '. 
26      

773$£  grai 
773*f  " 
773H  ' 

2 

2 
2 
2 

29  •»'•..' 
32      

43  •    •    •    •    • 

46 

773M  ' 
77381  ' 

774^  ' 

2 
2 
2 

49  
52    

56  ,.          .    . 

774*1  " 
774**  " 
774^-2  " 

2 

q8 

774#J  " 

2o  An  Inquiry  concerning 

Time  when  weighed.  Was  found  to  weigh. 

At3h.    im 774$ J  grains. 

3     18 774M      " 

*  3     25     .        .        .        .        .         .  774M      " 

6     15 774H      " 

Immediately  after  this  last-mentioned  weighing  of 
the  bullet,  the  whole  of  the  apparatus  appearing  to  have 
acquired  the  temperature  of  the  air  in  the  room  (60°  F.), 
the  bullet  was  taken  away,  and  the  porcelain  stand  and 
cup  were  again  balanced  in  the  scale,  when  it  appeared 
that  they  had  lost  \  of  a  grain  in  weight  during  the 
preceding  experiment.  This  apparent  loss  of  weight  I 
could  ascribe  to  nothing  but  to  the  thorough  drying  of 
the  cups  in  the  experiment  with  the  red-hot  bullet,  and 
to  the  drying  of  the  silk  cords  by  which  the  scale  con- 
taining the  cup  and  stand  was  suspended  to  the  arm  of 
the  balance. 

This  weight  =  \  of  a  grain,  which  was  required  to 
balance  the  scales  at  the  end  of  the  experiment,  being 
added  to  the  apparent  weight  of  the  bullet  at  6  h.  1 5  m. 
—  774ei>  *ts  true  weignt  at  that  time  appears  to  have 
been  775 J£. 

The  weight  of  the  bullet  at  I  h.  30  m.  having  been  no 
more  than  773^-  grains,  and  at  6  h.  15  m.  it  being  found 
to  weigh  775jf  grains,  it  appears  that  it  had  gained  in 
weight  by  being  heated  red-hot  775J-f  —  773  e6*  =  2i 
grains. 

This  augmentation  of  weight  doubtless  arose  from 
the  partial  oxidation  of  the  iron.  It  certainly  did  not 
arise  from  the  heat,  for  it  remained  after  the  bullet  had 
become  cold. 

*  Just  before  this  weighing,  the  coffee-cup  which  covered  the  bullet  in  the  scale 
had  been  removed  for  a  moment  to  look  at  the  bullet,  and  then  immediately  re- 
placed. What  it  was  that  escaped  on  this  occasion  I  will  not  undertake  to  say,  but 
certain  it  is  that  its  weight  amounted  to  -£•%  of  a  grain,  at  the  least; 


the  Weight  ascribed  to  Heat.  21 

An  Account  of  an  Experiment  made  with  a  Bullet  of  Fine  Gold. 

Munich,,  i^d  April,  1785.  —  Weather  cloudy,  with 
intervals  of  sunshine ;  thermometer  in  my  room  at 
65°  F  ;  barometer  at  26  inches  4  lines. 

A  small  bullet  of  fine  gold,  equal  in  value  to  10  Ger- 
man ducats,  which  I  procured  from  the  master  of  the 
mint,  being  weighed  in  the  open  air  of  my  room,  was 
found  to  weigh  477^  J  grains. 

The  small  open  china  cup,  in  which  the  bullet  was 
weighed,  was  exactly  counterbalanced  by  a  weight  = 
44°lf!  grains. 

At  10  h.  5  m.  A.  M.  the  bullet,  heated  to  a  clear  red 
heat  approaching  to  whiteness,  and  weighed  in  the  cup, 
open  to  the  air,  the  bullet  and  the  cup  together  were 
found  to  have  lost  of  their  weight  J|J  of  a  grain. 

Removing  the  bullet  immediately,  I  found  that  the 
cup,  or  rather  the  cup  and  the  scale  in  which  it  was 
placed,  together  had  lost  in  weight  ^-f  f  parts  of  a  grain. 

Consequently,  the  bullet  must  have  lost  of  its  weight 
by  being  heated  red-hot ;  or  it  appeared  to  be  lighter 
when  red-hot  than  when  cold  by  ^|F  parts  of  a  grain, 
or  fc-yj-g-  part  of  its  whole  weight. 

Upon  repeating  the  experiment  I  had  nearly  the 
same  result ;  but  upon  varying  it,  by  covering  the 
heated  bullet  in  the  scale,  in  different  ways,  I  found 
such  variations  in  the  results  as  convinced  me  that  the 
apparent  diminution  of  weight  above  mentioned  might 
easily  have  arisen  from  currents  in  the  atmosphere, 
and  consequently  that  no  dependence  can  be  placed 
in  experiments  of  that  kind  for  deciding  the  fact  rela- 
tive to  the  weights  of  heated  bodies,  or  the  ponder- 
ability of  heat. 


22  An  Inquiry  concerning  the  Weight  ascribed  to  Heat. 

I  afterwards  contrived  an  apparatus  for  making  the 
experiment  in  a  different  and  more  unexceptionable 
manner.  I  provided  three  hollow  globes  of  brass,  very 
thin,  and  one  larger  than  the  other,  and  which  being 
made  to  open  in  the  middle,  like  a  tobacco-box,  could 
be  placed  one  within  another.  In  the  centre  globe  I 
intended  to  place  a  solid  bullet  of  pure  gold,  red-hot. 
Between  the  centre  globe  and  that  next  it,  I  proposed 
to  leave  a  space  equal  to  the  diameter  of  the  heated 
bullet,  filled  with  air ;  and  the  space  between  the  sec- 
ond globe  and  the  third  I  meant  to  have  filled  with 
pounded  ice;  and  I  proposed  to  have  made  the  ex- 
periment at  a  time  when  the  heat  of  the  atmosphere 
should  be  just  equal  to  that  of  freezing  water;  and  in 
this  manner  I  conceived  that  I  should  be  able  to  avoid 
the  currents  in  the  air,  whose  effects  I  had  found  so 
distressing  in  my  former  experiments.  But  when  I 
considered  that  the  whole  of  the  heat  contained  by  the 
red-hot  bullet  would  not  be  sufficient  to  thaw  one  half 
of  the  ice  which  surrounded  it,  and  that,  when  the  bul- 
let should  be  cooled  to  the  temperature  of  the  ice,  the 
whole  mass  of  metal,  of  ice,  and  of  water,  would  still 
remain  at  the  -point  of  freezing ;  and,  moreover,  that 
weighing  the  water  produced  by  the  ice  would,  in  fact,  be 
weighing  the  heat  which  before  existed  in  the  red-hot 
bullet,  it  first  occurred  to  me  that  the  point  in  question 
might  much  more  readily  be  determined  by  simply 
weighing  a  quantity  of  ice  at  the  temperature  of  freezing, 
and  weighing  the  same  again  when  changed  into  water. 

I  therefore  left  my  apparatus  unfinished,  and  turned 
my  whole  attention  to  the  experiments  of  which  an 
account  has  been  given  in  the  former  part  of  this  paper. 

[This  paper  is  printed  from  Rumford's  Philosophical  Papers, 
pp.  366-383.] 


AN    INQUIRY 

CONCERNING    THE 

NATURE   OF   HEAT,  AND   THE   MODE   OF   ITS 
COMMUNICATION. 

HEAT  is  employed  in  such  a  vast  variety  of  differ- 
ent processes,  in  the  affairs  of  life,  that  every 
new  discovery  relative  to  it  must  necessarily  be  of  real 
importance  to  mankind ;  for,  by  obtaining  a  more  inti- 
mate knowledge  of  its  nature  and  mode  of  action,  we 
shall  no  doubt  be  enabled  not  only  to  excite  it  with 
greater  economy,  but  also  to  confine  it  with  greater 
facility,  and  direct  its  operations  with  more  precision 
and  effect. 

Having  many  years  ago  found  reason  to  conclude 
that  a  careful  observation  of  the  phenomena  which  at- 
tend the  heating  and  cooling  of  bodies,  or  the  communi- 
cation of  heat  from  one  body  to  another,  would  afford 
the  best  chance  of  acquiring  a  farther  insight  into  the 
nature  of  heat,  my  view,  in  all  my  researches  on  this 
subject,  has  been  principally  directed  to  that  point ; 
and  the  experiments  of  which  I  am  now  to  give  an 
account  may  be  considered  as  a  continuation  of  those 
I  have  already,  at  different  times,  had  the  honour  of 
laying  before  the  Royal  Society,  and  of  presenting  to 
the  public  in  my  Essays. 

In  order  that  the  attention  of  the  Society  may  not  be 


24        Inquiry  concerning  the  Nattire  of  Hcat> 

interrupted  unnecessarily  by  description  of  instruments 
in  the  midst  of  the  accounts  of  interesting  experiments, 
I  shall  begin  by  describing  the  apparatus  which  was 
provided  for  these  researches ;  and,  as  a  perfect  knowl- 
edge of  the  instruments  made  use  of  is  indispensably 
necessary  in  order  to  form  distinct  ideas  of  the  experi- 
ments, I  shall  take  the  liberty  to  be  very  particular  in 
these  descriptions. 

The  thermometers,  four  in  number,  which  were  used 
in  these  experiments,  were  constructed  under  my  own 
eye,  and  with  the  greatest  possible  care  ;  and,  after 
every  trial  I  have  been  able  to  make  with  them,  in 
order  to  ascertain  their  accuracy,  they  appear  to  be  very 
perfect. 

They  are  mercurial  thermometers,  graduated  accord- 
ing to  Fahrenheit ;  their  bulbs  are  cylindrical,  4  inches 
long,  and  -j4^-  of  an  inch  in  diameter ;  and  their  tubes 
are  from  15  to  16  inches  long.  The  mercury  with 
which  they  are  filled  is  quite  pure,  and  they  are  freed 
from  air.  Their  scales  were  divided  with  the  greatest 
care;  and,  by  means  of  a  nonius,  they  show  eighth 
parts  of  a  degree  very  distinctly;  they  are  graduated 
from  about  10  degrees  below  the  freezing  point  to  5 
or  6  degrees  above  the  point  of  boiling  water.  Their 
bulbs  are  quite  naked;  their  scales  ending  about  i 
inch  above  the  junction  of  the  bulb  with  its  tube.  The 
freezing  point  is  situated  about  5  inches  above  the 
upper  end  of  the  bulb.  The  reason  for  placing  it  so 
high  will  be  evident  from  the  details  of  the  experiments 
in  which  these  instruments  were  used. 

The  instrument  I  contrived  for  ascertaining  the 
warmth  of  clothing  is  extremely  simple ;  it  is  merely  a 
hollow  cylindrical  vessel  made  of  thin  sheet  brass.  It 


and  the  Mode  of  its  Communication.  25 

is  closed  at  both  ends,  and  has  a  narrow  cylindrical 
neck,  by  which  it  is  occasionally  filled  with  hot  water. 

This  vessel,  being  covered  with  a  garment  made  to 
fit  it,  composed  of  any  kind  of  cloth  or  stuff,  or  other 
warm  covering,  is  supported  in  a  vertical  position  on  a 
wooden  stand,  which  is  placed  on  a  table  in  a  large 
quiet  room ;  and  one  of  the  thermometers  above  de- 
scribed being  placed  in  the  axis  of  the  vessel,  the  time 
employed  in  cooling  the  water,  through  the  clothing 
with  which  the  instrument  is  covered,  is  observed  and 
noted  down. 

Now,  as  the  time  of  cooling  through  any  given  inter- 
val of  the  scale  of  the  thermometer  (or  from  any  given 
degree  above  the  temperature  of  the  air  of  the  room  to 
any  other  given  lower  degree,  but  still  above  the  tem- 
perature of  the  air  of  the  room)  will  be  longer  or 
shorter  as  the  covering  of  the  instrument  is  more  or 
less  adapted  for  confining  heat,  it  is  evident  that  the 
relative  warmth  of  clothing  of  different  kinds  may 
be  very  accurately  determined  by  experiments  of  this 
sort. 

I  provided  four  instruments  of  this  kind,  all  very 
nearly  of  the  same  dimensions.  Their  cylindrical  bodies 
are  each  4  inches  in  diameter  and  4  inches  long;  and 
their  cylindrical  necks  are  about  T87  of  an  inch  in  diam- 
eter, and  4  inches  in  length.  This  neck  is  placed  in 
the  centre  of  the  circular  flat  top,  or  upper  end,  of  the 
vertical  cylindrical  body ;  and  opposite  to  it,  in  the 
centre  of  the  flat  bottom  of  the  body,  there  is  a  hollow 
cylinder,  T8^  of  an  inch  in  diameter  and  3  inches  long, 
projecting  downwards,  into  which  a  vertical  cylinder  of 
wood  is  fitted,  on  the  top  of  which  the  instrument  is 
supported,  in  such  a  manner  that  the  air  has  free  access 


26        Inqiiiry  concerning  the  Nature  of  Heat, 

to  every  part  of  it.  This  cylinder  of  wood  constitutes 
a  part  of  the  wooden  stand  above  mentioned. 

As  the  thermometer  is  placed  in  the  axis  of  the  cylin- 
drical vessel,  and  as  its  bulb  is  just  as  long  as  the  body 
of  this  vessel,  it  is  evident  that  it  must  ever  indicate 
the  mean  temperature  of  the  water  in  the  vessel,  however 
different  the  temperature  of  that  water  may  be  at  differ- 
ent depths. 

The  thermometer  is  firmly  supported  in  its  place  by 
causing  a  part  of  the  lower  end  of  its  scale  to  enter  the 
neck  of  the  cylindrical  vessel,  and  to  fit  it  with  some 
degree  of  accuracy,  but  not  so  nicely  as  to  be  in  danger 
of  sticking  fast  in  it. 

The  lower  end  of  the  bulb  of  the  thermometer  does 
not  absolutely  touch  the  bottom  of  the  vessel,  but  it  is 
very  near  touching  it. 

Figure  i  (Plate  I.)  will  give  a  clear  idea  of  this 
instrument  placed  on  its  wooden  stand,  which  is  so  con- 
trived that  the  instrument  may  be  placed  higher  or 
lower  at  pleasure. 

The  foregoing  description  of  this  instrument  is  so 
particular  that  the  figure  will  be  easily  understood 
without  any  further  illustration.  The  cylindrical  vessel 
is  represented  placed  on  the  stand,  with  its  thermome- 
ter in  its  place. 

As,  in  some  of  the  first  experiments  I  made  with  this 
instrument,  I  found  it  difficult  to  apply  the  coverings 
which  I  used  to  the  ends  of  the  body  of  the  instru- 
ment, I  endeavoured,  by  covering  up  those  ends  with  a 
permanent  and  very  warm  covering,  to  oblige  most  of 
the  heat  to  pass  off  through  the  vertical  sides  of  the 
instrument,  to  which  it  was  easy  to  fit  almost  any  kind 
of  covering,  and  more  especially  coverings  of  various 


PLATE  I 


fSiy'J. 


and  the  Mode  of  its  Communication.  27 

thicknesses  of  confined  air,  the  relative  warmth  of 
which  I  was  very  desirous  of  ascertaining. 

The  means  I  employed  for  covering  up  the  ends  of 
the  instrument  were  as  follows.  Having  provided  two 
thin  cylindrical  wooden  boxes  (like  common  pill-boxes, 
but  much  larger),  something  less  in  diameter  than  the 
body  of  the  instrument,  and  2-J-  inches  deep,  I  dried 
them  as  much  as  possible ;  and,  after  having  varnished 
them  within  and  without  with  spirit  varnish,  I  covered 
them  within  and  without  with  fine  wove  writing-paper, 
and  then  gave  the  paper  three  coats  of  the  same  varnish. 
I  then  perforated  the  bottoms  of  these  boxes  with 
round  holes,  just  large  enough  to  admit  the  neck  of  the 
instrument,  and  the  cylindrical  projection  at  its  bot- 
tom ;  and  then  inverted  them  over  the  two  ends  of  the 
instrument,  filling  the  boxes  at  the  same  time  with 
eider-down. 

These  boxes  were  fixed  and  confined  in  their  places 
by  means  easy  to  be  imagined  ;  and,  in  order  to  con- 
fine the  heat  still  more  effectually,  each  of  the  boxes 
was  covered  on  the  outside  with  a  cap  of  fur,  as  often 
as  the  instrument  was  used;  as  was  also  that  part- of 
the  neck  of  the  instrument  which  projected  above  the 
box. 

Two  of  the  instruments,  which  I  shall  distinguish  by 
the  numbers  i  and  2,  were  covered  up  at  their  ends  in 
this  manner;  the  other  two  instruments,  No.  3  and 
No.  4,  were  left  in  the  state  represented  by  the  Figure 
i ;  that  is  to  say,  the  ends  of  their  cylindrical  bodies 
were  not  covered  with  permanent  coverings. 

In  each  experiment,  two  similar  instruments  (No.  i 
and  No.  2,  for  instance,  or  No.  3  and  No.  4)  were 
used,  the  one  naked^  and  the  other  covered;  and,  as  the 


•28        Inquiry  concerning  the  Nature  of  Heat., 

naked  instrument  always  served  as  a  standard,  with 
which  the  results  of  the  experiments  made  with  the 
other  were  compared,  it  is  evident  that  this  arrange- 
ment rendered  the  general  results  of  the  experiments 
much  more  satisfactory  and  conclusive  than  they  could 
possibly  have  been,  had  the  experiments  made  on  differ- 
ent days  and  with  various  kinds  of  covering  been 
made  singly,  or  unaccompanied  by  a  fixed  and  invari- 
able standard. 

The  experiments  were  made  and  registered  in  the 
following  manner:  The  two  instruments  used  in  the 
experiment,  placed  on  their  wooden  stands,  being  set 
down  on  the  floor,  were  filled  to  within  about  \\  inch 
of  the  tops  of  their  cylindrical  necks  with  boiling  hot 
water ;  and,  a  thermometer  being  put  into  each  of  them, 
they  were  placed  at  the  distance  of  three  feet  from  each 
other,  on  a  large  table,  in  a  corner  of  a  large  quiet 
room,*  where  they  were  suffered  to  cool  undisturbed. 
Near  them  on  the  same  table,  and  at  the  same  height 
above  the  table,  there  was  placed  another  thermometer 
(suspended  in  the  air  to  the  arm  of  a  stand),  by  which 
the  temperature  of  the  air  of  the  room  was  ascertained 
from  time  to  time. 

No  person  was  permitted  to  pass  through  the  room 
while  an  experiment  was  going  on ;  and  in  order  to 
prevent,  as  far  as  it  was  possible,  all  those  currents  of 
air  in  the  room  which  were  occasioned  by  partial  heat, 
produced  by  the  light  which  came  in  at  the  windows, 
the  window-shutters  were  kept  constantly  shut ;  one  of 
them  only  being  opened  for  a  moment,  now  and  then, 
just  to  observe  the  thermometers,  and  note  down  the 
progress  of  the  experiment. 

*  This  room,  which   is  adjoining  to  my  laboratory,  in  my  house  at  Munich,  is  19 
feet  wide,  24  feet  long,  and  13  feet  high. 


and  the  Mode  of  its  Communication.  29 


The  results  of  each  experiment  were  entered  on  a 
separate  sheet  of  paper  ;  which  paper  was  previously 
prepared  for  that  use  by  being  divided  into  separate 
vertical  columns  by  lines  drawn  with  a  pen,  and  ruled 
in  parallel  horizontal  lines  with  a  lead-pencil. 

"  Experiments  on  Heat,  made  at  Munich,  nth  March,  1803.  The 
large  cylindrical  Vessels,  No.  I  and  No.  2  (made  of  thin  sheet  brass), 
were  filled  with  hot  Water,  and  exposed  to  cool  in  the  Air  of  a  large 
quiet  Room.  The  Ends  of  both  these  Instruments  were  well  covered 
with  warm  Clothing,  Furs,  &c.  The  vertical  polished  Sides  of 
No.  I  were  naked.  The  Sides  of  No.  2  were  covered  with  one 
Thickness  of  fine  white  Irish  Linen,  which  had  been  worn, 
strained  over  the  metallic  Surface." 


Time. 

Temperature 

Tem- 
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of  the 
Air. 

Time. 

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min. 

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An  end  was  now  put  to  the  experiment. 

The  above  is  an  exact  copy  of  one  of  these   regis- 


30        Inquiry  concerning  the  Nature  of  Heat, 

ter-sheets,  and  contains  the  results  of  an  actual  and  very 
interesting  experiment,  which  lasted  26  hours. 

Though  it  was  easy  to  discover,  by  a  single  glance  at 
the  register,  whether  a  covering  which  was  put  over 
one  of  the  instruments  prolonged  the  time  of  its  cool- 
ing or  not;  yet,  in  order  to  compare  the  results  of  dif- 
ferent experiments,  and  particularly  of  such  as  were 
made  on  different  days,  so  as  to  determine  with  pre- 
cision how  much  warmer  one  kind  of  covering  was  than 
another,  it  was  necessary  to  fix  on  some  particular  in- 
terval in  the  scale  of  the  thermometer,  or  number  of 
degrees,  commencing  at  some  certain  invariable  number 
of  degrees  above  the  temperature  of  the  'air  by  which 
the  instrument  was  surrounded,  in  order  that  the 
warmth  of  the  covering,  or  its  power  of  confining  heat, 
might  with  certainty  be  estimated  by  the  time  employed 
in  cooling  through  that  interval. 

By  the  results  of  a  great  number  of  experiments  I 
found  that  the  same  instrument  cooled  through  any 
given  (small)  number  of  degrees  (10  degrees,  for  in- 
stance) in  very  nearly  the  same  time,  whatever  was  the 
temperature  of  the  air  of  the  room  ;  provided  always, 
that  the  point  from  which  these  10  degrees  commenced 
was  at  the  same  given  number  of  degrees  above  the 
temperature  of  the  air  at  the  time  being. 

The  interval  I  chose  for  comparing  the  results  of  my 
experiments  is  that  which  commences  with  the  fiftieth, 
and  ends  with  the  fortieth,  degree  of  Fahrenheit's  ther- 
mometer above  the  temperature  of  the  air  in  which  the  in- 
strument is  exposed  to  cool  When,  for  instance,  the  air 
was  at  58°,  the  interval  commenced  at  the  io8th  degree, 
and  ended  at  the  98th.  When  the  air  was  at  64^°,  it 
commenced  at  114^°,  and  ended  at  104!°. 


and  t/ie  Afode  of  its  Communication.  31 

That  the  same  instrument,  exposed  to  cool  in  the 
air,  does  in  fact  cool  the  same  number  of  degrees  in  the 
same  time,  very  nearly,  when  the  given  interval  of  the 
scale  of  the  thermometer  is  reckoned  from  the  same 
height,  or  given  number  of  degrees  above  the  tempera- 
ture of  the  air  at  the  time  when  the  experiment  is  made, 
will  appear  from  the  following  results  of  1  1  different 
experiments,  made  on  different  days,  and  when  the  air 
in  which  the  instrument  was  exposed  to  cool  was  at  dif- 
ferent degrees  of  temperature. 

The  large  cylindrical  vessel,  No.  i,  having  its  two 
ends  well  covered  up  with  eider-down,  furs,  &c.,  its 
vertical  sides  being  exposed  naked  to  the  air,  in  a  large 
quiet  room,  was  found  to  cool  10  degrees,  viz.  from  the 
5Oth  to  the  4Oth  degree  above  the  temperature  of  the  air 
in  which  it  was  exposed,  as  follows  :  — 


44 

.     from  94     to  84 

45* 

. 

95i  to  85^ 

48 

" 

98    to  88 

5!i 

ii 

ioii  to  91^ 

52 

" 

102      tO  92 

54 

" 

104    to  94 

44 

" 

94    to  84 

42* 

M 

92^  to  82^ 

45 

" 

95    to  85 

46 

" 

96    to  86 

44 

M 

94    to  84 

55     minutes. 


551       «« 
55          " 


..     56 

.         55 


The  fact  which  these  experiments  are  here  brought 
to  prove  has  likewise  been  confirmed  by  other  experi- 
ments, made  with  other  instruments,  and  at  times  when 
the  temperature  of  the  air  has  been  as  high  as  64°;  but 
I  will  not  take  up  the  time  of  the  Society  by  giving  a 
particular  account  of  them  in  this  place. 


32         Inquiry  concerning  the  Nature  of  Heat, 

As  it  sometimes  happened,  though  very  seldom,  in 
the  course  of  an  experiment  (which  commonly  lasted 
several  hours)  that  I  was  called  away,  and  was  not  pres- 
ent to  observe  the  thermometer  at  the  moment  of  the 
passage  of  the  mercury  through  one  or  both  of  those 
points  of  its  scale  which  formed  the  limits  of  the  given 
interval  chosen  as  the  standard  for  a  comparison  of  the 
results  of  the  experiments  with  each  other,  it  became  a 
matter  of  considerable  importance  to  find  means  for 
supplying  these  accidental  defects,  and  ascertaining  the 
points  in  question  by  interpolation. 

In  order  to  facilitate  the  means  of  doing  this,  I  en- 
deavoured to  investigate  the  law  of  the  cooling  of  hot 
bodies  in  a  cold  fluid  medium ;  and  I  found  reason  to 
conclude, 


M 


That  if,  on  the  right  line  AB,  a  perpendicular  CD  be 
taken,  equal  to  the  difference  of  the  temperatures  of  the 
hot  body  and  of  the  colder  medium,  expressed  in  de- 
grees of  the  thermometer ;  and,  after  a  certain  given 
time,  represented  by  CE,  taken  on  the  line  AB  at  the 


and  the  Mode  of  its  Communication*          33 

point  E,  another  perpendicular  EF  be  erected,  and  EF 
be  taken  equal  to  the  difference  of  the  temperatures 
after  the  time  represented  by  CE  has  elapsed;  and  if 
the  perpendiculars  GH  and  LM  be  drawn,  representing 
the  difference  of  the  temperatures  after  the  times  EG 
and  GL  have  elapsed,  a  curved  line  PQ  drawn  through 
the  points  D,  F,  H,  M,  will  be  the  logarithmic  curve; 
or,  if  it  vary  from  that  curve,  its  variation,  within 
the  limits  answering  to  a  change  of  temperature  amount- 
ing to  a  few  degrees  (especially  if  they  be  taken  when 
the  temperature  of  the  hot  body  is  about  40  or  50 
degrees  above  that  of  the  medium),  will  be  so  very 
small  that  no  sensible  error  will  result  from  a  supposi- 
tion that  it  is  the  logarithmic  curve,  in  supplying,  by 
computation,  any  intermediate  observations  which  hap- 
pen to  have  been  neglected  in  making  an  experiment. 

These  computations  are  very  easily  made,  with  the 
assistance  of  a  ta"ble  of  logarithms,  in  the  following 
manner. 

Supposing  CD,  CG,  and  GH,  to  have  been  deter- 
mined by  actual  observation  ;  and  that  it  were  required 
to  ascertain,  by  computation,  the  absciss  CE,  corres- 
ponding to  any  given  intermediate  ordinate  EF,  or 
(which  is  the  same  thing)  to  determine  at  what  time  the 
cooling  body  was  at  any  given  intermediate  temperature 
(=  EF)  between  that  (=  CD)  which  it  was  found  by 
observation  to  have  at  the  point  C,  and  that  (=  GH) 
which  it  was  found  to  have  after  the  time  represented  by 
the  line  GC  had  elapsed  ; 

It  is  log.  CD  —  log.  GH  is  to  CG  as  i  to  m 
(=  modulus  =  the  subtangent  of  the  curve  at  the  point 
D.)*  And  CE  =  m  X  log.  CD  —  log.  EF. 

*  The  subtangent  shows  in  what  time  the  instrument  would  cool  down  to  the  tem- 
VOL.   II.  3 


34        Inquiry  concerning  the  Nature  of  Heat, 

If,  for  instance,  in  the  experiment  of  the  nth  March, 
(the  details  of  which  have  just  been  given)  the  time 
when  the  instrument  No.  2,  in  cooling,  passed  the 
important  point  of  94°  had  not  been  observed,  this 
neglect  might  have  been  supplied,  by  computation,  in 
the  following  manner. 

It  is  CD  =  94f°,  the  nearest  observed  temperature 
higher  than  EF  (=  94°),  and  GH  =  9oJ,  the  nearest 
observed  temperature  below  that  of  94°  ;  and  CG  =  15 
minutes,  or  900  seconds  =  the  time  elapsed  between 
the  two  observations. 

It  is  log.  94!  =  1.9765792 
And  log.  90^  —  1.9554472 

Log.  CD  —  log.  GH  =  0.021 1320 

And  0.0211320  is  to  900  (=  CG)  as  i  to  42590  =  m. 

And  again,  log.  94!  —  1.9765792 
Log.  94    =  1.9731279 

Log.  CD  —  log.  EF  =  0.0034513 

42590  X  0.0034513  (=mX  log.  CD  —  log.  EF)  = 
147  seconds  =  2  minutes  and  27  seconds;  which  dif- 
fers very  little  from  2j  minutes,  the  observed  time. 

If,  from  the  temperature  observed  at  nh.  30  min.  = 
86J°,  and  the  temperature  observed  at  nh.  45  min.  = 
82^°,  and  the  time  which  elapsed  between  these  two 

perature  of  the  air  in  which  it  is  placed,  were  its  velocity  of  cooling  at  the  point  D  to 
be  continued  uniformly  from  that  point;  and,  as  the  subtangent  of  the  logarithmic 
curve  is  constant,  if  PQ  were  the  logarithmic  curve,  it  would  follow  that  the  velocity 
with  which  a  hot  body  cools  in  a  fluid  medium  is  everywhere  such,  that,  were  that 
•velocity  to  be  continued  uniformly,  the  body  would  be  cooled  down  to  the  temperature 
of  the  medium  in  the  same  time,  whatever  might  be  the  excess  of  the  temperature  of 
the  hot  body  above  that  of  the  medium,  at  the  moment  when  its  velocity  of  cooling 
became  uniform. 


and  the  Mode  of  its  Communication.  35 

observations  (=  15  minutes),  we  were  to  determine  by 
computation  the  time  when  the  instrument  was  at  the 
temperature  of  84°  (the  lower  point  of  the  standard 
interval  of  10  degrees  answering  to  the  temperature  of 
the  air,  =  44°,  in  which  the  instrument  was  cooled),  it 
will  turn  out,  8  minutes  and  55  seconds  after  nh. 
30  min.  The  observed  time  was  nh.  39  min. ;  which 
differs  from  the  computed  time  no  more  than  5  seconds. 

If  it  were  strictly  true,  as  a  very  great  philosopher 
and  mathematician  has  advanced,  that  the  velocity  with 
which  a  hot  body,  exposed  to  cool  in  a  cold  fluid  me- 
dium, parts  with  its  heat  is  as  the  difference  of  the  tem- 
peratures of  the  body  and  of  the  medium,  it  is  most  cer- 
tain that  the  curve  PQ  could  be  no  other  than  the  loga- 
rithmic curve.  Perhaps  it  may  be  so  in  fact,  and  that 
the  variations  from  it  which  my  experiments  indicated 
were  owing  solely  to  the  imperfection  of  the  divisions 
of  our  thermometers.  If  it  be  so,  it  is  not  impossible 
to  divide  the  scale  of  a  thermometer  in  such  a  manner 
as  to  indicate  with  certainty  equal  increments  of  heat,  as 
thermometers  ought  to  do  ;  but  this  is  not  the  proper 
place  to  enlarge  on  this  subject.  I  may  perhaps  return 
to  it  hereafter. 

Passing  over  in  silence  a  number  of  experiments  I 
made  in  order  to  get  thoroughly  acquainted  with  my 
new  instruments,  and  to  assure  myself  that  the  results 
of  similar  experiments  made  with  them  were  uniform 
and  might  be  depended  on,  I  shall  now  proceed  to  give 
an  account  of  several  experiments  made  with  pointed 
views,  the  results  of  some  of  which  were  very  inter- 
esting. 

Experiment  No.  i.  —  The  large  cylindrical  vessel  No.  i, 
with  its  ends  covered  with  warm  clothing,  in  the  man- 


36  Inquiry  concerning  the  Nature  of  Heat, 

ner  before  described,  and  its  vertical  sides  (which  were 
polished,  and  very  clean  and  bright)  exposed  naked  to 
the  air,  was  filled  with  water  nearly  boiling  hot,  and 
placed  on  its  wooden  stand,  on  a  table,  in  a  large  quiet 
room  to  cool ;  the  air  of  the  room  being  at  the  tem- 
perature of  45°  Fahrenheit. 

Another  cylindrical  vessel,  No.  2,  in  all  respects  like 
No.  i,  and  with  its  ends  covered  in  the  same  manner, 
but  with  its  vertical  sides  covered  with  a  single  covering 
of  fine  Irish  linen  (such  as  is  sold  in  London  for  about 
4  s.  per  yard),  closely  applied  to  the  body  of  the  instru- 
ment, was  filled  with  hot  water  at  the  same  time,  and 
placed  on  the  same  table  to  cool. 

This  experiment  lasted  many  hours ;  and,  in  that 
period,  the  temperature  of  the  water  in  each  of  the 
instruments  was  carefully  observed  and  noted  down  a 
great  number  of  times. 

The  result  of  this  experiment  (the  details  of  which 
have  already  been  given)  was  very  remarkable. 

While  the  instrument  No.  i,  whose  sides  were  naked, 
employed  55  minutes  in  cooling  from  the  point  of  94° 
to  that  of  84°,  the  instrument  No.  2,  whose  sides  were 
covered  with  linen,  cooled  through  the  same  interval  in 
36!  minutes. 

Hence  it  appears  that  clothing  may,  in  some  cases, 
expedite  the  passage  of  heat  out  of  a  hot  body,  instead 
of  confining  it  in  it. 

Desirous  of  seeing  whether  the  same  covering  would, 
or  would  not,  expedite  the  passage  of  heat  into  the  in- 
strument, after  having  suffered  both  instruments  to 
cool  down  to  the  temperature  of  about  42°,  I  removed 
them  into  a  warm  room,  in  which  the  air  was  at  the 
temperature  of  62°;  and  I  found  that  the  instrument 


and  the  Mode  of  its  Communication.  37 

No.  2,  which  was  clothed,  acquired  heat  considerably 
faster  than  the  other,  No.  i,  which  was  naked.* 

The  discovery  of  these  extraordinary  facts  surprised 
me,  and  excited  all  my  curiosity ;  and  I  immediately 
set  about  investigating  their  cause. 

As  it  is  well  known  that  air  adheres  with  consider- 
able obstinacy  to  the  surfaces  of  some  solid  bodies,  I 
conceived  it  to  be  possible  that  the  particles  of  air  in 
immediate  contact  with  the  surface  of  the  cylindrical 
vessel  No.  I,  might  in  fact  be  so  attached  to  the  metal 
as  to  adhere  to  it  with  some  considerable  force ;  and,  if 
that  were  the  case,  as  confined  air  is  known  to  consti- 
tute a  very  warm  covering,  it  appeared  to  me  to  be 
possible  that  the  cooling  of  the  vessel  No.  i  might 
have  been  retarded  by  such  an  invisible  covering  of 
confined  air;  which  covering,  in  the  experiment  with 
the  vessel  No.  2,  had  been  displaced  and  in  a  great 
measure  driven  away  by  the  colder  covering  of  linen 
by  which  the  body  of  the  instrument  was  closely  em- 
braced. 

I  conceived  that  the  linen  must  have  accelerated  the 
cooling  of  the  instrument,  either  by  facilitating  the 
approach  of  a  succession  of  fresh  particles  of  cold  air, 
or  by  increasing  the  effects  of  radiation;  and,  with  a 
view  to  elucidate  that  important  point,  the  following 
experiments  were  made. 

Experiment  No.  2.  —  Removing  the  linen  with  which 
the  instrument  No.  2  was  clothed,  I  now  covered  the 
sides  of  that  instrument  with  a  thin  transparent  coat- 
ing of  glue ;  and,  when  it  was  quite  dry  and  hard, 
I  again  filled  the  two  instruments  (No.  i  and  No.  2) 

*  The  details  of  this  experiment  (which  was  made  on  the  nth  of  March,  1803) 
may  be  seen  on  page  29. 


347888 


38        Inquiry  concerning  the  Nature  of  Heat, 

with  hot  water,  and  observed  the  times  of  their  cooling 
as  before. 

Result,  or  time  of  cooling  10  degrees,  reckoned  from 
the  50th  to  the  4Oth  degree  above  the  temperature 
of  the  air  in  which  the  instruments  were  exposed  to 
cool : — 

Instrument  No.  I,  sides  naked,    .         .          .          .          -55     min- 
Instrument  No.  2,  sides  covered  with  one  coating  of  glue,    431    " 

When  we  consider  this  experiment  with  attention, 
we  shall  find  reason  to  conclude,  that  if  it  were  by  facili- 
tating the  approach  and  temporary  contact  of  a  succes- 
sion of  fresh  particles  of  the  cold  air  of  the  room  to  the 
surface  of  the  glue  (which  was  now  in  fact  become  the 
surface  of  the  hot  body),  that  the  cooling  of  the  instru- 
ment was  accelerated,  the  metal  being  as  completely 
covered,  and  the  air,  supposed  to  be  attached  and  fixed 
to  its  surface,  as  completely  excluded  by  one  coating  of 
the  glue  as  it  could  be  by  two  or  more,  two  coatings 
could  not  possibly  accelerate  the  cooling  of  the  instru- 
ment more  than  one  ;  but  if,  on  the  other  hand,  the 
cooling  of  the  instrument  in  this  experiment  was  ac- 
celerated, not  by  facilitating  and  accelerating  the  mo- 
tions of  the  circumambient  cold  air,  but  by  facilitat- 
ing and  increasing  those  radiations  which  are  known  to 
proceed  from  hot  bodies,  I  conceived  that  two  coat- 
ings of  the  glue  might  possibly  accelerate  the  cooling 
of  the  vessel  more  than  one.  In  order  to  put  this  con- 
jecture to  the  test,  I  made  the  following  decisive  experi- 
ment. 

Experiment  No.  3.  —  I  now  gave  the  instrument  No.  2 
a  second  coating  of  glue;  and,  when  it  was  thoroughly 
dry,  I  repeated  the  experiment  last  mentioned,  with  the 


and  the  J\lode  of  its  Commiinication.  39 

above  variation  ;   when  I  found  the  results  to  be  as  fol- 
lows :  — 

Time  of  cooling 

the    10   degrees 

in  question. 

The  instrument  No.  I,  naked  metal,   .          .         .         .     55^  min. 
The  instrument  No.  2,  covered  vi\\h.  two  coatings  of  glue,   37^    " 

Finding  that  two  transparent  coatings  of  glue  facili- 
tated the  cooling  of  this  instrument  even  more  than 
one  coating,  I  washed  off  all  the  glue  with  warm  water ; 
then,  making  the  instrument  as  clean  and  bright  as  pos- 
sible, I  covered  its  sides  with  a  coating  of  very  fine, 
transparent,  and  colourless  spirit  varnish ;  and,  after 
this  coating  of  varnish  had  become  quite  dry  and  hard, 
I  repeated  the  experiment  above  mentioned  ;  and,  find- 
ing that  this  covering,  like  that  of  glue,  expedited  the 
cooling  of  the  instrument,  I  first  added  a  second  coat- 
ing of  the  varnish,  and  repeated  the  experiment  again, 
and  then  added  two  coatings  more,  making  four  in  all. 
Finding  that  the  cooling  of  the  instrument  was  more 
and  more  rapid;  as  the  thickness  of  the  varnish  was 
increased,  I  now  added  four  coatings  more,  making 
eight  coatings  in  the  whole,  giving  time  for  each  new 
coating  to  dry  thoroughly  before  the  next  was  applied ; 
but  I  found,  on  repeating  the  experiment  with  this 
thick  covering  of  varnish,  that  I  had  passed  the  limit 
of  thickness  which  produced  the  greatest  effect. 

In  order  that  the  result  of  these  experiments  with 
coatings  of  different  thicknesses  of  spirit  varnish  may 
be  seen  at  one  view,  I  shall  here  place  them  all  to- 
gether ;  and  I  shall  place  by  the  side  of  each  the  result 
of  the  standard  experiment,  which  was  made  at  the  same 
time  with  the  instrument  No.  I,  the  sides  which  were 
naked. 


40        Inquiry  concerning  the  Nature  of  Heat, 

Time  employed  in  cooling  through 
the  given  interval  of  10  degrees. 
Instrument  Instrument 

No.  i,  No.  2, 

varnished.  naked. 

Experiment  No.  4.  —  I  coating  of  varnish,  42  min.  55^  min. 

Experimented.  5. —  2  coatings,          .         •  35t  "  55i     " 

Experiment  No.  6. — 4  coatings,     .          .  30^  "  55!    " 

Experiment  No.  7. —  8  coatings,         .          .  34^  "  55        " 

Experiment  No.  8.  —  Desirous  of  finding  out  what 
effect  colour  would  produce,  I  now  painted  the  sides  of 
the  instrument  No.  1  black,  with  lamp-black  mixed  up 
'with  size  (this  paint  being  laid  upon  the  eighth  coating 
of  the  varnish),  and,  repeating  the  experiment,  its  re- 
sults were  as  follows  :  — 

Time   employed  in 

cooling  through  the 

given  interval. 

The  instrument  No.  I,  naked,  .          .          .          .          •      55i  rnin. 
The  instrument  No.  2,  covered  with  8  coatings  of  var- 
nish, and  painted  black,    .         .         .          .          .  34       " 

Experiment  No.  9.  —  Finding  that  the  painting  of  this 
thick  coating  of  varnish  black  rendered  the  covering 
still  colder,  or  accelerated  the  cooling  of  the  instrument, 
I  now  washed  off  the  black  paint  with  warm  water; 
then  washing  off  all  the  varnish  with  hot  spirit  of  wine, 
I  painted  the  metallic  sides  of  the  instrument  of  a  black 
colour  with  lamp-black  and  size ;  and  when  the  paint 
was  quite  dry,  I  repeated  the  experiment  so  often  men- 
tioned, when  the  results  were  as  follows  :  — 

Time  employed  in 

cooling  through  the 

given  interval. 

The  instrument  No.  I,  sides  naked,    .         .         .         .     55^  min. 
The  instrument  No.  ^,  painted  black,       .          .         .          35       " 

Experiment  No.  10.  —  In  order  to  find  out  whether 
the  black  colour  had  any  particular  efficacy  in  expediting 
the  cooling  of  the  instrument,  or  whether  another  colour- 
ing substance  would  not  produce  the  same  effect,  when 


and  the  Mode  of  its  Communication.  41 

mixed  up  with  the  same  size,  I  now  washed  off  the 
black  paint  and  painted  the  sides  of  the  instrument 
white y  with  whiting  mixed  up  with  size  ;  and,  on  repeat- 
ing the  experiment,  the  results  were  as  follows  :  — 

Time  of  cooling  through 
the  given  interval. 

The  instrument  No.  I,  naked,   .          .          .          .          •      55a  nrin. 
The  instrument  No.  i,  painted  white,      .          .          .          36       " 

As  in  both  the  two  last  experiments  it  was  found 
necessary  to  paint  the  body  of  the  instrument  three  or 
four  times  over,  in  order  to  cover  the  polished  metal  so 
completely  as  to  prevent  its  shining  through  the  paint ; 
this,  of  course,  occasioned  the  surface  of  the  metal  to  be 
covered  with  a  thick  coating  of  size,  which,  no  doubt, 
affected  very  sensibly  the  results  of  the  experiment,  and 
rendered  it  impossible  to  determine,  in  a  satisfactory 
manner,  what  the  effects  really  were,  which  were  pro- 
duced by  the  different  colours  used  in  the  two  experiments. 

Experiment  No.  1 1 .  —  With  a  view  to  throw  some  more 
light  on  this  interesting  subject,  having  washed  off  the 
paint  from  the  instrument  No.  2,  I  now  rendered  its 
sides  of  a  perfectly  deep  black  colour,  by  holding  it  over 
the  flame  of  a  wax  candle ;  and,  repeating  the  usual  ex- 
periment, the  results  were  as  follows  :  — 

Time  of  cooling  through 
the  standard  interval. 

The  instrument  No.  I,  naked, 55!  min. 

The  instrument  No.  2,  blackened,    .  36^    " 

In  order  to  ascertain  the  quantity  of  matter  which 
composed  this  black  covering,  I  weighed  a  small  piece 
of  clean  and  very  fine  linen ;  and,  having  wiped  off 
with  it  all  the  black  matter  from  the  body  of  the  instru- 
ment No.  2,  in  such  a  manner  that  the  whole  of  it  re- 
mained attached  to  the  linen,  I  weighed  it  again,  and 


42         Inquiry  concerning  the  Nature  of  Pleat, 

by  that  means  discovered  that  the  whole  of  this  black 
substance,  which  had  so  completely  covered  the  sides 
of  the  instrument  (a  surface  of  polished  brass  =  50 
superficial  inches)  that  the  metal  did  not  shine  through 
it  in  any  part,  weighed  no  more  than  T^  of  a  grain 
Troy. 

How  this  very  thin  covering,  which,  if  the  specific 
gravity  of  the  black  matter  were  only  equal  to  that  of 
water,  would  amount  to  no  more  than  ?-£$-§  of  an  inch 
in  thickness,  could  expedite  the  cooling  of  the  instru- 
ment, in  the  manner  it  was  found  to  do,  is  what  still 
remains  to  be  shown ;  but,  before  I  proceed  any  farther 
in  these  abstruse  inquiries,  I  shall  make  a  few  observa- 
tions relative  to  the  results  of  the  foregoing  experi- 
ments. 

Although  we  may  with  safety  presume,  that  the  ve- 
locities with  which  the  heat  escaped  through  the  sides  of 
the  instruments  *  were  nearly  as  the  times  inversely  taken 
up  in  cooling  through  the  given  interval  of  10  degrees  ; 
yet,  as.  some  heat  must  have  made  its  way,  in  the  course 
of  the  experiment,  through  the  ends  of  the  instrument, 
notwithstanding  all  the  care  that  was  taken  to  prevent 
it  by  covering  them  up  with  warm  clothing,  it  is 
necessary,  in  order  to  be  able  to  compare  the  results  of 
the  preceding  experiments  in  a  satisfactory  manner,  to 

*  I  have  found  myself  obliged  in  this,  as  in  many  other  places,  to  make  use  of  lan- 
guage which  is  far  from  being  as  correct  as  I  could  wish.  I  do  not  believe  that  heat 
ever  makes  its  escape  in  the  manner  here  indicated ;  but  I  could  not  venture  to  use 
uncommon  expressions  in  pointing  out  the  phenomena  in  question,  however  well 
adapted  such  expressions  might  be  to  describe  the  events  which  really  take  place.  If 
it  should  be  found  that  caloric,  like  phlogiston,  is  merely  a  creature  of  the  imagination, 
and  has  no  real  existence  (which  has  ever  appeared  to  me  to  be  extremely  probable), 
in  that  case,  it  must  be  incorrect  to  speak  of  heat  as  making  its  escape  out  of  one  body, 
and  passing  into  another ;  but  how  often  are  we  obliged  to  use  incorrect  and  figurative 
language,  in  speaking  of  natural  phenomena  ! 


and  the  Mode  of  its  Communication*          43 

find  out  how  much  of  the  heat  made  its  escape  through 
the  covered  ends  of  the  instruments,  during  the  time 
the  instruments  were  cooling  through  the  interval  in 
question. 

In  order  to  determine  that  point,  I  now  removed  the 
covering  from  the  ends  of  the  instrument  No.  i  ;  and, 
when  it  was  quite  naked,  I  found,  on  making  the  ex- 
periment, that  it  cooled  through  the  given  interval  in 
45^  minutes. 

When  its  two  ends  and  its  cylindrical  neck  were  cov- 
ered up  with  warm  clothing,  I  found,  by  taking  the 
mean  of  the  results  of  several  experiments,  that  it  re- 
quired 55J  minutes  to  cool  through  the  same  interval. 

On  measuring  the  instrument  with  care,  I  found  its 
dimensions  as  follows  :  — 

Inches. 

Diameter  of  the  body  of  the  instrument,         .  .     =  4.03 
Length  of  the  body,           .'.»,.         ss  3.96 

Diameter  of  the  neck  of  the  instrument,         .  .     =  0.8 
Length  of  the  neck,           .         .         .         .         .         =  4- 

The  superficies  of  the  different  parts  of  the  instru- 
ment are  therefore  as  follows  :  — 

Superficies  of  the  vertical  sides  of  the  body  (=  4.03 

X  3-HJ59  X  3-96)  —  S°-136  inches. 

Superficies  of  the  flat  circular  bottom  of  the  instru- 
ment, (—4.03  X  3-I4I59  X  ^)  =  12.755  inches;  de- 
ducting nothing  for  that  part  which  is  covered  by  the 
end  of  the  tube,  which  serves  as  a  support  for  the 
instrument. 

Superficies  of  the  flat  circular  top  of  the  instrument 
(after  deducting  0.502  of  a  superficial  inch  for  the  cir- 
cular hole  in  its  centre,  made  to  receive  the  lower  end 
of  the  cylindrical  neck)  =  12.253  inches. 


44        Inquiry  concerning  the  Nature  of  Heat, 

Superficies  of  the  cylindrical  neck  of  the  instrument 
(=  0.8  X  3.HI59  X  4)  =  10-051  inches. 

Supposing,  now,  that  the  heat  passes  with  equal  ve- 
locity through  the  surface  of  all  the  different  parts  of  the 
instrument,  when  the  instrument  is  naked,  we  can  deter- 
mine the  quantity  of  heat  which  escaped  through  the 
ends  and  neck  of  the  instrument  in  the  experiments  in 
which  those  parts  of  the  instrument  were  covered  with 
warm  clothing. 

The  whole  of  the  metallic  surface  exposed  to  the  air, 
in  the  experiments  made  with  the  instrument  when  it 
was  quite  naked,  amounted  to  85.195  superficial  inches, 
namely :  — 

Inches. 

Surface  of  its  vertical  sides,  .  .  .  .  =50.136 
Surface  of  its  lower  end,  .  .  .  .  =12.755 
Surface  of  its  upper  end,  .  .  .  .  =  12.253 

Surface  of  its  neck,       .....=  10.051 

Total  surface, =85.195 

When  the  instrument  was  exposed  quite  naked  to  the 
air,  it  was  found  to  cool  through  the  standard  interval 
of  10  degrees  in  45^-  minutes. 

Assuming,  now,  any  given  number  as  the  measure  of 
the  whole  quantity  of  heat  given  ofT  by  the  instrument 
during  the  period  above  mentioned,  we  can  ascertain 
what  part  or  proportion  of  that  quantity  passed  off 
through  the  sides  of  the  instrument ;  and  what  part  of 
it  must  have  made  its  escape  through  its  ends,  and 
through  the  sides  of  its  neck. 

As  the  quantities  of  heat  given  off  are  supposed  to 
have  been  as  the  quantities  of  surface  exposed  to  the 
air,  if  we  suppose  the  whole  quantity  of  heat  lost  by 
the  instrument  to  be  =  10,000  parts,  the  quantity  which 


and  tlie  Mode  of  its  Communication.  45 

passed  through  the  vertical  sides  of  the  instrument  in 
45!  minutes,  in  the  experiment,  must  have  amounted 
to  5885  parts.  For,  the  whole  of  the  surface  of  the 
instrument,  =  85.195  superficial  inches,  is  to  the  whole 
of  the  heat  given  off,  =  10,000,  as  the  surface  of  the 
vertical  sides  of  the  instrument,  =  50.136  superficial 
inches,  to  the  quantity  of  heat  which  must  have  passed 
off  through  that  surface  in  the  given  time,  =  5885. 

Now,  as  we  may  with  safety  conclude  that  the  quan- 
tity of  heat  which  passes  off  through  a  given  surface 
must  be  as  the  times  elapsed,  all  other  circumstances 
being  the  same,  we  can  determine  how  much  of  the  heat 
given  off  by  the  instrument,  in  those  experiments  in 
which  its  ends  were  covered,  passed  through  the  sides 
of  the  instrument ;  and,  consequently,  how  much  of  it 
must  have  made  its  way  through  its  ends  and  neck,  not- 
withstanding their  being  covered: 

The  instrument  with  its  ends  and  neck  covered  up 
with  eider-down,  furs,  &c.,  was  found  to  cool  through 
the  standard  interval  of  10  degrees  in  55!  minutes. 
Now,  as  only  5885  parts  of  heat  were  found  to  pass 
through  the  naked  vertical  sides  of  the  instrument  in 
45 \  minutes,  no  more  than  7015  parts  could  have 
passed  through  the  same  surface  in  55^  minutes  ;  con- 
sequently, the  remainder  of  the  heat  lost  by  the  instru- 
ment in  the  experiment  in  question,  amounting  to 
2985  parts,  must  necessarily  have  made  its  way  through 
the  covered  ends  and  neck  of  the  instrument  in  the 
given  period,  55}  minutes. 

Taking  it  for  granted  that  these  computations  are 
well  founded,  we  may  now  proceed  to  a  more  exact  de- 
termination of  the  relative  quantities  of  heat  which 
made  their  way  through  the  sides  of  the  instrument 


46        Inquiry  concerning  the  Nature  of  Heat, 

No.  2,  when  its  sides  were  exposed  naked  to  the  air, 
and  when  they  were  covered  with  the  different  sub- 
stances which  appeared  to  facilitate  the  escape  of  the 
heat. 

In  the  experiment  No.  n,  when  the  sides  of  the  in- 
strument were  made  quite  black  by  holding  it  over  the 
flame  of  a  wax  candle,  the  instrument  cooled  through 
the  standard  interval  of  10  degrees  in  36^  minutes. 

In  that  time  a  quantity  of  heat  =  1942  parts  must 
have  passed  off  through  the  covered  ends  and  neck  of 
the  instrument;  for,  if  a  quantity  =  2985  parts  could 
pass  off  that  way  in  55-!  minutes,  the  quantity  above 
mentioned  (=  1942  parts)  must  have  escaped  in  36^ 
minutes. 

This  quantity,  =  !942  parts,  taken  from  the  whole 
quantity,  =  10,000  parts,  lost  by  the  instrument  in 
cooling  through  the  interval  in  question,  leaves  8058 
parts  for  the  quantity  which  made  its  escape  through 
the  sides  of  the  instrument  in  the  experiment  in 
question. 

Now,  if  a  quantity  of  heat  =  7015  parts,  requires 
55^-  minutes  to  make  its  way  through  the  naked  sides 
of  the  instrument  (as  we  have  just  seen),  it  would 
require  63 f  minutes  for  the  quantity  in  question,  = 
8058  parts,  to  pass  off  through  the  same  surface. 

But,  when  that  surface  was  blackened  over  the  flame 
of  a  candle,  that  quantity  of  heat  passed  off  through  it 
in  36^  minutes. 

Hence  it  appears,  that  the  velocity  with  v/hich  heat  is 
given  off  from  the  naked  surface  of  a  heated  metal  ex- 
posed to  cool  in  the  air,  is  to  the  velocity  with  which  it 
is  given  off  by  the  same  metal  when  its  surface  is  black- 
ened in  the  manner  above  described,  as  36^  to  63!,  or 


and  the  Mode  of  its  Communication.  47 

as  5654  to  10,000,  very  nearly ;  for  the  velocities  are  as 
the  times  of  cooling,  inversely. 

Again,  in  the  experiment  No.  6,  the  sides  of  the  in- 
strument No.  i  being  covered  with  four  coatings  of 
spirit  varnish,  the  instrument  was  found  to  cool  through 
the  given  interval  of  10  degrees  in  30^  minutes. 

In  that  time,  a  quantity  of  heat  =  1627  parts,  must 
have  made  its  way  through  the  covered  ends  of  the  in- 
strument ;  and  the  remainder,  =  8373  parts,  must  have 
made  its  way  through  its  varnished  sides. 

This  quantity,  =  8373  parts,  would  have  required 
66|  minutes  to  have  made  its  way  through  the  naked 
sides  of  the  instrument ;  and,  as  it  actually  made  its 
way  through  the  varnished  sides  of  the  instrument  in 
30^  minutes,  it  appears  that  the  velocity  with  which 
the  heat  was  given  off  from  the  naked  metallic  surface, 
was  to  the  velocity  with,  which  it  was  given  off  from 
the  same  surface  covered  with  four  coatings  of  spirit 
varnish,  as  66 \  to  30^,  or  as  10,000  to  4566. 

Without  pursuing  these  computations  any  farther  at 
present,  and  without  stopping  to  make  any  remarks  on 
the  curious  facts  they  present  to  us,  I  shall  hasten  to 
experiments,  from  the  results  of  which  we  shall  obtain 
more  satisfactory  information.  But,  before  I  proceed 
any  farther,  I  must  give  an  account  of  an  instrument  I 
contrived  for  measuring,  or  rather  for  discovering,  those 
very  small  changes  of  temperature  in  bodies,  which  are 
occasioned  by  the  radiations  of  other  neighbouring 
bodies,  which  happen  to  be  at  a  higher  or  at  a  lower 
temperature.  , 

This  instrument,  which  I  shall  take  the  liberty  to 
call  a  ther  mo  scope  ^  is  very  simple  in  its  construction. 
Like  the  hygrometer  of  Mr.  Leslie  (as  he  has  chosen 


48        Inquiry  concerning  the  Nature  of  Heat, 

to  call  his  instrument),  it  is  composed  of  two  glass 
balls,  attached  to  the  two  ends  of  a  bent  glass  tube;  but 
the  balls,  instead  of  being  near  together,  are  placed  at 
a  considerable  distance  from  each  other ;  and  the  tube 
.which  connects  them,  instead  of  being  bent  in  its  mid- 
dle, and  'its  two  extremities  turned  upwards,  is  quite 
straight  in  the  middle,  and  its  two  extremities,  to  which 
its  two  balls  are  attached,  are  turned  perpendicularly 
upwards,  so  as  to  form  each  a  right  angle  with  the  mid- 
dle part  of  the  tube,  which  remains  in  a  horizontal 
position. 

At  one  of  the  elbows  of  this  tube  there  is  inserted  a 
short  tube  of  nearly  the  same  diameter,  by  means  of 
which  a  very  small  quantity  of  spirit  of  wine,  tinged 
of  a  red  colour,  is  introduced  into  the  instrument ;  and, 
after  this  is  done,  the  end  of  this  short  tube  (which  is 
only  about  an  inch  long)  is  sealed  hermetically ;  and  all 
communication  is  cut  off  between  the  air  in  the  balls 
of  the  instrument  and  in  its  tube  and  the  external  air 
of  the  atmosphere. 

A  small  bubble  of  the  spirit  of  wine  (if  I  may  be 
allowed  to  use  that  expression)  is  now  made  to  pass 
out  of  the  short  tube  into  the  long  connecting  tube  ; 
and  the  operation  is  so  managed  that  this  bubble 
(which  is  about  f  of  an  inch  in  length)  remains  station- 
ary, at  or  near  the  middle  of  the  horizontal  part  of  the 
tube,  when  the  temperature  (and  consequently  the  elasticity} 
of  the  air  in  the  two  balls,  at  the  two  extremities  of  the  tube, 
is  precisely  the  same. 

By  means  of  a  scale  of  equal  parts,  attached  to  the 
horizontal  part  of  the  connecting  tube,  the  position 
of  the  bubble  can  be  ascertained,  and  its  movements 
observed. 


and  the  Mode  of  its  Communication.  49 

If  now,  the  bubble  being  at  rest  in  its  proper  place, 
one  of  the  balls  of  the  instrument  be  exposed  to  the 
calorific  rays  which  proceed  in  all  directions  from  a  hot 
body,  while  the  other  ball  is  defended  from  those  rays 
by  a  screen,  the  air  in  the  ball  so  exposed  to  the  action 
of  these  rays  will  be  heated ;  and,  its  elasticity  being 
increased  by  this  additional  heat,  its  pressure  will  no 
longer  be  counterbalanced  Dy  the  elasticity  of  the  colder 
air  in  the  other  ball,  and  the  bubble  will  be  forced  to 
move  out  of  its  place  and  to  take  its  station  nearer  to 
the  colder  ball. 

By  presenting  two  hot  bodies  at  the  same  time  to 
the  two  balls  of  the  instrument,  taking  care  that  each 
ball  shall  be  defended  from  the  action  of  the  hot  body 
presented  to  the  opposite  ball,  the  distances  of  these 
hot  bodies  from  their  respective  balls  may  be  so  regu- 
lated that  their  actions  on  those  balls  may  be  equal, 
however  the  temperatures  of  those  hot  bodies  may 
differ,  or  however  different  may  be  the  quantities  or 
intensities  of  the  calorific  rays  which  they  emit. 

The  instrument  will  show,  with  the  greatest  certainty, 
when  the  actions  of  these  hot  bodies  on  their  respective 
balls  are  equal ;  for,  until  they  become  unequal,  the 
bubble  will  remain  immovable  in  its  place. 

And,  when  the  actions  of  two  hot  bodies  on  the 
instrument  are  equal,  the  relative  intensities  of  the  rays 
they  emit  may  be  ascertained  by  the  distances  of  the 
bodies  from  the  balls  of  the  ;nstrument. 

If  their  distances  from  their  respective  balls  are  equal, 
the  intensities  of  the  rays  they  emit  must,  of  course,  be 
equal. 

If  those  distances  are  unequal,  the  intensities  will 
probably  be  as  the  squares  of  the  distances,  inversely. 

VOL.    II.  4 


5O        Inquiry  concerning  the  Nature  of  Heat, 

A  distinct  and  satisfactory  idea  may  be  formed  of  the 
instrument  I  have  been  describing,  from  Fig.  2  (Plate  1 1.). 

AB  is  a  board,  27  inches  long,  9  inches  wide,  and  i 
inch  thick,  which  serves  as  a  support  for  the  bent  tube 
CDE,  at  the  two  extremities  of  which  the  two  balls  are 
fixed.  The  two  projecting  ends  of  the  tube,  C  and  E, 
which  are  in  a  vertical  position,  are  each  10  inches 
long ;  and  the  horizontal  part  D  of  the  tube,  which  is 
fastened  down  on  the  board,  is  17  inches  in  length. 

The  balls  are  each  1.625  inches  in  diameter.  The 
diameter  of  the  tube  is  such,  that  i  inch  of  it  in  length 
would  contain  15  grains  Troy  of  mercury. 

The  pillar  F,  which,  by  means  of  a  horizontal  arm 
projecting  from  it,  serves  for  supporting  the  circular 
vertical  screen  represented  in  the  figure,  is  firmly  fixed 
in  the  board  AB. 

This  circular  screen  (which  is  made  of  pasteboard, 
covered  on  both  sides  with  gilt  paper)  serves  for  pre- 
venting one  of  the  balls  of  the  instrument  from  being 
affected  by  the  calorific  rays  proceeding  from  a  hot  body 
which  is  presented  to  the  opposite  ball. 

Besides  the  circular  screen  represented  in  the  figure, 
several  other  screens  are  used  in  making  experiments  ; 
for  the  instrument  is  so  extremely  sensible,  that  the 
naked  hand  presented  to  one  of  the  balls,  at  the  dis- 
tance of  several  inches,  puts  -the  bubble  in  motion  ;  and 
it  is  affected  very  sensibly  by  the  rays  which  proceed 
from  the  person  who  approaches  it  to  make  the  experi- 
ments, unless  care  be  taken,  by  the  interposition  of 
screens,  to  prevent  those  rays  from  falling  on  the  balls. 
These  screens  can  be  best  and  most  readily  made  by 
providing  light  wooden  frames,  about  two  feet  square, 
and  half  an  inch  in  thickness,  and  covering  them  on 


:>&CO. 


and  the  Mode  of  its  Communication.  51 

both  sides,  first  with  thick  cartridge  paper,  and  then 
with  what  is  called  gilt  paper;  the  metallic  substance 
(copper)  with  which  one  side  of  the  paper  is  covered 
being  on  the  outside. 

To  support  a  movable  screen  of  this  kind  in  a  ver- 
tical position,  it  must  of  course  be  provided  with  a  foot 
or  stand.  Those  I  use  are  fastened  to  one  side  of  a 
pillar  of  wood  by  two  screws,  one  of  which  passes 
through  the  centre  of  the  screen  where  the  cross-bars 
belonging  to  the  frame  of  the  screen  meet,  and  the 
other  through  the  middle  of  the  piece  of  wood  which 
forms  the  bottom  of  the  screen.  This  pillar  of  wood, 
which  is  turned  in  a  lathe,  is  I2-|-  inches  high,  and 
is  firmly  fixed,  at  its  lower  end,  in  a  piece  of  wood 
8  inches  square  and  i  inch  thick,  which  serves  as  a  stand 
or  foot  for  supporting  it. 

As,  in  making  experiments  with  this  thermoscope,  it  is 
frequently  necessary  to  remove  the  hot  bodies  that  are 
presented  to  it  farther  from  it  or  to  bring  them  nearer 
to  it,  in  order  that  this  may  be  done  easily  and  expedi- 
tiously  by  one  person,  and  without  its  being  necessary 
for  him  to  remove  his  eye  from  the  bubble  (which  he 
should  constantly  have  in  his  view),  I  make  use  of  a 
simple  machine,  which  I  have  found  to  be  very  useful. 

It  is  a  long  and  shallow  wooden  box,  open  at  both 
ends.  It  is  6  feet  long,  12  inches  wide,  and  5  inches 
deep,  measured  on  the  outside ;  its  vertical  sides  are 
made  of  ij-inch  deal;  its  bottom  and  top,  of  inch  deal. 
A  part  only  of  the  top  or  cover  of  this  box  is  fixed 
down  on  the  sides,  and  is  immovable.  The  part  of 
the  cover  which  is  fixed,  and  on  which  the  thermoscope 
is  placed,  occupies  the  middle  of  the  box,  and  is  13 
inches  in  length.  On  the  right  and  left  of  this  fixed 


52         Inquiry  concerning  the  Nature  of  Heat, 

part,  the  top  of  the  box  is  covered  by  a  sliding  board, 
1  feet  3  inches  long,  which  passes  in  deep  grooves,  made 
to  receive  it,  in  the  sides  of  the  box.  A  rack  is  fixed 
to  the  under  side  of  each  of  these  sliding  boards  ;  and 
there  is  a  small  cog  wheel  in  the  box,  the  axis  of  which 
passes  through  the  sides  of  the  box,  and  is  furnished 
with  a  winch  in  the  front  of  the  box.  By  turning  round 
these  wheels  by  means  of  their  winches  (both  of  which 
can  be  managed  by  the  same  person,  at  the  same  time), 
the  sliders  may  be  moved  backwards  and  forwards  at 
pleasure. 

In  order  to  ascertain  with  facility  and  dispatch  the 
distances  of  the  hot  bodies  from  their  respective  balls, 
the  top  of  the  front  side  of  the  wooden  box  is  divided 
into  inches  on  each  side  of  the  fixed  part  of  the  cover 
of  the  box ;  and  there  is  a  nonius  belonging  to  each  of 
the  sliders,  which  is  placed  in  such  a  manner  as  to  indi- 
cate, at  all  times,  the  exact  distance  of  the  hot  body 
from  its  corresponding  ball. 

The  level  of  the  upper  surface  of  that  part  of  the 
cover  which  is  fixed  is  about  J  of  an  inch  higher  than 
the  level  of  the  upper  surface  of  the  sliders,  in  order 
that,  when  a  thermoscope  longer  than  this  fixed  part  is 
placed  on  it,  the  sliders  may  pass  freely  under  its  two 
projecting  ends  without  deranging  it. 

It  is  evident,  from  this  description,  that  by  placing 
the  thermoscope  on  the  fixed  part  of  the  cover  of  the 
box,  with  its  two  balls  in  a  line  parallel  to  the  axis  of 
the  box,  and  by  placing  the  two  hot  bodies  presented 
to  the  two  balls  of  the  instrument  (elevated  to  a  proper 
height)  on  stands  set  down  on  the  s-liders,  an  observer, 
by  taking  the  two  winches  in  his  hands,  keeping  his 
eye  fixed  on  the  bubble,  may,  with  the  greatest  facility, 


and  the  Mode  of  its  Communication.  53 

so  regulate   the  distances  of  the  hot  bodies  from  their 

O 

respective  balls  that  the  bubble  shall  remain  immov- 
able in  its  place. 

In  order  to  be  able  to  ascertain  precisely  the  tem- 
peratures of  the  hot  bodies  presented  to  this  instru- 
ment, and  in  order  that  their  surfaces  might  be  equal, 
two  equal  cylindrical  vessels,  of  thin  sheet  brass,  with 
oblique  cylindrical  necks,  were  provided,  of  the  form 
represented  in  Figure  3  (Plate  II.). 

This  cylindrical  vessel,  which  is  placed  in  a  horizon- 
tal position  in  order  that  its  flat  bottom  may  be  pre- 
sented in  a  vertical  position  to  one  of  the  balls  of  the 
thermoscope,  is  so  fixed  to  a  wooden  stand,  of  a  pecu- 
liar construction,  that  it  may  be  raised  or  lowered  at 
pleasure.  This  is  necessary,  in  order  that  its  axis  may 
be  in  the  continuation  of  a  line  passing  through  the 
centres  of  the  two  balls  of  the  thermoscope. 

This  cylindrical  vessel  is  3  inches  in  diameter  and  4 
inches  in  length,  and  its  oblique  cylindrical  neck  is 
O.86  of  an  inch  in  diameter  and  3.8  inches  in  length. 

The  neck  of  this  vessel  is  inserted  obliquely  into  its 
cylindrical  body,  in  order  that  the  water  with  which  it 
is  occasionally  filled  may  not  run  out  of  it,  when  the 
body  of  the  vessel  is  laid  down  in  a  horizontal  posi- 
tion, in  the  manner  represented  in  the  above-mentioned 
figure. 

A  thermometer,  with  a  cylindrical  bulb  4  inches  in 
length,  being  inserted  into  the  body  of  this  vessel, 
through  its  neck,  shows  the  temperature  of  the  con- 
tained water. 

Care  is  necessary,  in  constructing  a  thermoscope,  to 
choose  a  tube  of  a  proper  diameter;  if  its  bore  be  too 
small,  it  will  be  found  very  difficult  to  keep  the  spirit 


54        Inquiry  concerning  the  Nature  of  Heat, 

of  wine  in  one  mass;  and  if  it  be  too  large,  the  little 
horizontal  column  it  forms  (which  I  have  called  a  bub- 
ble) will  be  ill  defined  at  its  two  ends,  which  will  ren- 
der it  difficult  to  ascertain  its  precise  situation.  After 
a  number  of  trials  I  have  found  that  a  tube,  the  bore 
of  which  is  of  such  a  size  that  I  inch  of  it  in  length 
contains  about  15  or  18  grains  Troy  of  mercury,  an- 
swers best.  For  a  tube  of  that  size  the  balls  may  be 
about  i J  inch  in  diameter;  and  they  should  both  be 
painted  black  with  Indian  ink,  which  renders  the  in- 
strument more  sensible. 

I  have  an  instrument  of  this  kind,  the  tube  of  which 
is  quite  filled  with  spirit  of  wine,  excepting  only  the 
space  occupied  by  a  small  bubble  of  air,  which  is  in- 
troduced into  the  middle  of  the  horizontal  part  of  the 
tube;  but  it  does  not  answer  so  well  as  those  which 
contain  only  a  very  small  quantity  of  that  liquid,  suf- 
ficient to  form  a  small  bubble. 

But,  without  enlarging  any  farther,  at  present,  on 
the  construction  of  these  instruments,  I  now  proceed  to 
give  an  account  of  the  experiments  for  which  they  were 
contrived. 

Having  found  abundant  reason  to  conclude,  from  the 
results  of  the  experiments  of  which  an  account  has 
already  been  given,  that  all  the  heat  which  a  hot  body 
loses  when  it  is  exposed  in  the  air  to  cool  is  not  given 
off  to  the  air  which  comes  into  contact  with  it,  but  that 
a  large  proportion  of  it  escapes  in  rays,  which  do  not 
heat  the  transparent  air  through  which  they  pass,  but, 
like  light,  generate  heat  only  when  and  where  they  are 
stopped  and  absorbed,  —  I  suspected  that  in  every  case 
when,  in  the  foregoing  experiments,  the  cooling  of  my 
instruments  was  expedited  by  coverings  applied  to  their 


and  the  Mode  of  its  Communication.  55 

metallic  surfaces,  those  coverings  must,  by  some  means 
or  other,  have  facilitated  and  accelerated  the  emission 
of  calorific  rays  from  the  hot  surface. 
'  Those  suspicions  implied,  it  is  true,  the  supposition 
that  different  substances,  heated  to  the  same  tempera- 
ture, emit  unequal  quantities  of  calorific  rays  ;  but  I 
saw  no  reason  why  this  might  not  be  the  case  in  fact ; 
and  I  hastened  to  make  the  following  experiments, 
which  put  the  matter  beyond  all  doubt. 

Experiment  No.  11.  —  Two  equal  cylindrical  vessels, 
made  of  sheet  brass,  and  polished  very  bright,  each 
3  inches  in  diameter  and  4  inches  long,  suspended  by 
their  oblique  necks  in  a  horizontal  position  (being 
placed  on  their  wooden  stands),  were  filled  with  water  at 
the  temperature  of  180°;  and  their  circular  flat  bottoms 
were  presented  in  a  vertical  position  to  the  two  balls 
of  the  thermoscope,  at  the  distance  of  2  inches. 

When  the  two  hot  bodies  were  presented,  at  the  same 
moment,  to  the  two  balls  of  the  instrument,  or,  what 
was  still  better,  when  two  screens  were  placed  before 
the  two  balls,  at  the  distance  of  about  an  inch,  and, 
after  the  hot  bodies  were  placed,  these  screens  were 
both  removed  at  the  same  instant,  the  small  column  of 
spirit  of  wine,  which  I  have  called  a  bubble.,  remained 
immovable  in  its  place,  in  the  middle  of  the  horizontal 
part  of  the  tube  of  the  instrument. 

If  one  of  the  hot  bodies  was  now  brought  nearer  the 
ball  to  which  it  was  presented  (the  other  hot  body  re- 
maining in  its  place),  the  bubble  immediately  began  to 
move  from  the  hot  body  which  was  advanced  forward, 
towards  the  opposite  ball  to  which  the  other  hot  body 
was  presented. 

If,  instead  of  advancing  one  of  the  hot  bodies  nearer 


56         Inquiry  concerning  the  Nature  of  Heat, 

the  ball  to  which  it  was  presented,  it  was  drawn  back- 
ward to  a  greater  distance  from  it,  the  action  of  its  calo- 
rific rays  on  the  ball  was  diminished  by  this  increase  of 
distance  ;  and,  being  overcome  by  the  action  of  the  rays 
from  the  hot  body  presented  to  the  opposite  ball  (at  a 
smaller  distance),  the  bubble  was  forced  out  of  its 
place,  and  obliged  to  move  towards  the  ball  which  had 
•been  drawn  backward. 

When  one  of  the  hot  bodies  only  was  presented  to 
one  of  the  balls,  the  bubble  was  immediately  put  in 
motion,  and  by  bringing  the  hot  body  nearer  to  the 
ball,  it  might  be  driven  quite  out  of  the  tube  into  the 
opposite  ball ;  this,  however,  should  never  be  done,  be- 
cause it  totally  deranges  the  instrument,  as  it  is  easy  to 
perceive  it  must  do. 

Having,  by  these  trials,  ascertained  the  sensibility 
and  the  accuracy  of  my  instrument,  I  now  proceeded  to 
make  the  following  decisive  experiment. 

Experiment  No.  13. —  Having  blackened  the  flat  cir- 
cular bottom  of  one  of  the  cylindrical  vessels  by  hold- 
ing it  over  the  flame  of  a  wax  candle,  I  now  filled  both 
vessels  again  with  water  at  the  temperature  of  i8o°F., 
and  presented  them,  as  before,  to  the  two  opposite  balls 
of  the  instrument  at  equal  distances. 

The  bubble  was  instantly  driven  out  of  its  place  by 
the  superior  action  of  the  blackened  surface,  and  did 
not  return  to  its  former  station  till  after  the  vessel 
which  was  blackened  had  been  removed  to  more  than  8 
inches  from  the  ball  to  which  it  was  presented  ;  the 
other  vessel,  which  had  not  been  blackened,  remaining 
in  its  former  situation,  at  the  distance  of  2  inches  from 
its  ball. 

The   result  of  this    experiment  appeared    to   me    to 


and  t/M  Mode  of  its   Communication.  57 

throw  a  new  light  on  the  subject  which  had  so  long 
engaged  my  attention,  and  to  present  a  wide  and  very 
interesting  field  for  farther  investigation. 

I  could  now  account,  in  a  manner  somewhat  more 
satisfactory,  for  those  appearances  in  the  foregoing  ex- 
periments which  were  so  difficult  to  explain,  —  for  the 
acceleration  of  the  passage  of  the  heat  out  of  my  instru- 
ments, which  resulted  from  covering  them  with  linen, 
varnish,  &c. ;  and  .1  immediately  set  about  making  a 
variety  of  new  experiments,  from  which  I  conceived  I 
should  acquire  a  farther  insight  into  those  invisible 
mechanical  operations  which  take  place  when  bodies  are 
heated  and  cooled. 

Finding  so  great  a  difference  in  the  quantities  of  calo- 
rific rays  which  are  thrown  off  by  the  polished  surface 
of  a  metal  when  exposed  naked  to  the  cold  air  and 
when  blackened^  I  now  proceeded  to  make  experiments  to 
ascertain  whether  or  not  all  those  substances  with  which 
the  sides  of  my  cylindrical  vessels  had  been  covered,  and 
which  had  been  found  to  expedite  the  cooling  of  those 
instruments,  would  also  facilitate  the  emission  of  calo- 
rific rays  from  the  surfaces  of  the  instruments  I  pre- 
sented to  the  balls  of  my  thermoscope  ;  and  I  found 
this  to  be  the  case  in  fact. 

As  the  results  of  all  these  experiments  proved,  in  the 
most  decisive  manner,  that  all  the  substances  which, 
when  applied  to  the  metallic  surfaces  of  my  large  cylin- 
drical vessels,  had  expedited  their  cooling,  facilitated  and 
expedited  the  emission  of  calorific  rays,  I  could  no 
longer  entertain  any  doubts  respecting  the  agency  of 
radiation  in  the  heating  and  cooling  of  bodies.  Many 
important  points,  however,  still  remained  to  be  investi- 
gated before  distinct  and  satisfactory  ideas  could  be 


58         Inquiry  concerning  the  Nature  of  Heat, 

formed  respecting  the  nature  of  those  rays  and  the 
mode  of  their  action. 

I  had  hitherto  made  use  of  but  one  metal  (brass)  in 
my  experiments  ;  and  that  was  not  a  simple,  but  a  com- 
pound metal.  The  first  subject  of  inquiry  which  pre- 
sented itself,  in  the  prosecution  of  these  researches,  was 
to  find  out  whether  or  not  similar  experiments  made 
with  other  metals  would  give  similar  results. 

Experiment  No.  14.  —  Procuring  from  a  gold-beater  a 
quantity  of  leaf  goid  and  leaf  silver  about  three  times 
as  thick  as  that  which  is  commonly  used  by  gilders,  I 
covered  the  surfaces  of  the  two  large  cylindrical  vessels, 
No.  i  and  No.  2,  with  a  single  coating  of  oil  varnish ; 
and,  when  it  was  sufficiently  dry  for  my  purpose,  I  gilt 
the  instrument  No.  i  with  the  gold  leaf,  and  covered  the 
other,  No.  2,  with  silver  leaf.  When  the  varnish  was  per- 
fectly dry  and  hard,  I  wiped  the  instruments  with  cotton, 
to  remove  the  superfluous  particles  of  the  gold  and  sil- 
ver, and  then  repeated  the  experiment,  so  often  mentioned, 
of  filling  the  instruments  with  boiling-hot  water,  and 
exposing  them  to  cool  in  the  air  of  a  large  quiet  room. 

The  time  of  cooling  through  the  given  interval  of 
10  degrees  was  just  the  same  as  it  was  before,  when  the 
natural  surface  of  these  brass  vessels  was  exposed  naked 
to  the  air.  1  repeated  the  experiment  several  times, 
but  could  not  find  that  the  difference  in  the  metals 
made  any  difference  in  the  times  of  cooling. 

Experiment  No.  15.  —  Not  satisfied  to  rest  the  deter- 
mination of  so  important  a  point  on  a  trial  with  three 
metals  only,  —  brass,  gold,  and  silver,  —  I  now  provided 
myself  with  two  new  instruments,  —  the  one  made  of 
lead,  and  the  other  covered  with  tinned  sheet-iron,  im- 
properly, in  England,  called  tin. 


and  the  Mode  of  its  Communication.  59 

As  the  conducting  power  of  lead,  with  respect  to  heat, 
is  much  greater  than  that  of  any  other  metal,  I  con- 
ceived that,  if  the  radiation  of  a  body  were  any  way 
connected  with  its  conducting  power,  the  cooling  of  the 
water  contained  in  the  leaden  vessel  would  necessarily 
be  either  more  or  less  rapid  than  in  a  vessel  constructed 
of  any  other  metal. 

The  result  of  this  experiment,  as  also  the  results  of 
several  others  similar  to  it,  showed  that  heat  is  given 
off  with  the  same  facility,  or  with  the  same  celerity, 
from  the  surfaces  of  all  the  metals. ' 

Is  not  this  owing  to  their  being  all  equally  wanting 
in  transparency  ?  And  does  not  this  afford  us  a  strong 
presumption  that  heat  is  in  all  cases  excited  and  com- 
municated by  means  of  radiations,  or  undulations,  as  I 
should  rather  choose  to  call  them  ? 

I  am  sensible,  however,  that  there  is  another  and 
most  important  question  to  be  decided  before  these 
points  can  be  determined ;  and  that  is,  whether  bodies 
are  cooled  in  consequence  of  the  rays  they  emit  or  by 
those  they  receive. 

The  celebrated  experiment  of  Professor  Pictet,  which 
has  often  been  repeated,  appears  to  me  to  have  put  the 
fact  beyond  all  doubt,  that  rays,  or  emanations,  which, 
like  light,  may  be  concentrated  by  concave  mirrors, 
proceed  from  cold  bodies ;  and  that  these  rays,  when  so 
concentrated,  are  capable  of  affecting,  in  a  manner  per- 
fectly sensible,  a  delicate  air  thermometer. 

One  of  the  objects  I  had  principally  in  view,  in  con- 
triving the  before-described  instrument,  which  I  have 
called  a  thermoscope,  was  to  investigate  the  nature  and 
properties  of  those  emanations,  and  to  find  out,  if  pos- 
sible, whether  they  are  not  of  the  same  nature  as  those 


60  Inquiry  concerning  the  Nature  of 

calorific  rays  which  have  long  been  known  to  proceed 
from  hot  bodies. 

My  first  attempts,  in  these  investigations,  were  to 
ascertain  the  existence  of  those  emanations  universally, 
and  to  discover  what  visible  effects  they  might  be  made 
to  produce  independently  of  concentration  by  means 
of  concave  mirrors. 

Experiment  No.  16.  —  My  two  horizontal  cylindrical 
vessels  of  sheet  brass  (of  the  same  form  and  dimen- 
sions), having  been  made  very  clean  and  bright,  were 
fixed  to  their  stands  ;  and,  being  elevated  to  a  proper 
height  to  be  presented  to  the  balls  of  the  thermoscope, 
were  set  down  near  that  instrument  (which  was  placed 
on  a  table  in  a  large  quiet  room),  where  they  were  suf- 
fered to  remain  several  hours,  in  order  that  the  whole 
of  this  apparatus  might  acquire  precisely  the  same  tem- 
perature. 

Daylight  was  excluded  by  closing  the  window-shut- 
ters ;  and,  in  crder  that  the  thermoscope  might  not  be 
deranged  by  the  calorific  rays  proceeding  from  the  person 
of  the  observer  on  his  entering  the  room  to  complete 
the  intended  experiments,  screens  were  previously  placed 
before  the  instrument  in  such  a  manner  that  its  balls 
were  completely  defended  from  those  rays. 

Things  having  been  thus  prepared,  I  entered  the 
room  as  gently  as  possible,  in  order  not  to  put  the  air 
of  the  room  in  motion,  and,  approaching  the  thermo- 
scope, presented  first  one  and  then  the  other  cylin- 
drical vessel  to  one  of  the  balls  of  the  instrument ;  but 
it  was  not  in  the  least  degree  affected  by  them,  the  bub- 
ble of  spirit  of  wine  remaining  immovably  in  the  same 
place. 

Experiment  No.  17.  —  Having  assured  myself,  by  these 


and  the  Mode  of  its  Communication.  61 

previous  trials,  that  the  instrument  was  not  sensibly 
affected  by  a  bright  metallic  surface  being  presented  to 
it,  provided  the  temperature  of  the  metal  and  that  of 
the  instrument  were  the  same,  I  now  withdrew  one  of 
the  cylindrical  vessels,  and,  taking  it  into  another  room, 
I  filled  it  with  pounded  ice  and  water. 

Entering  the  room  again,  I  now  presented  the  flat 
vertical  bottom  of  this  horizontal  cylindrical  vessel, 
filled  with  ice  and  water,  to  one  of  the  balls  of  the  ther- 
moscope  at  the  distance  of  four  inches. 

The  bubble  of  spirit  of  wine  began  instantly  to 
move  with  a  slow,  regular  motion  towards  the  cold 
body  ;  and,  having  advanced  in  the  tube  about  an  inch, 
it  remained  stationary. 

On  bringing  the  cold  body  nearer  the  ball  to  which  it 
was  presented,  the  bubble  was  again  put  in  motion,  and 
advanced  still  farther  towards  the  cold  body. 

Experiment  No.  18.  —  Although  the  result  of  the  fore- 
going experiment  appeared  to  me  to  afford  the  most 
indisputable  proof  of  the  radiation  of  cold  bodies,  and 
that  the  rays  which  proceed  from  them  have  a  power  of 
generating  cold  in  warmer  bodies  which  are  exposed  to 
their  influence,  yet  in  a  matter  so  extremely  curious, 
and  of  such  high  importance  to  the  science  of  heat,  I 
was  not  willing  to  rest  my  inquiries  on  the  result  of  a 
single  experiment. 

In  order  to  vary  the  substance,  or  species  of  matter, 
presented  cold  to  the  instrument,  and  at  the  same  time 
to  remove  all  suspicion  respecting  the  possibility  of  the 
effects  observed  being  produced  by  currents  of  cold  air 
occasioned  in  the  room  by  the  presence  of  the  cold 
body,  I  now  repeated  the  experiment  with  the  following 
variations. 


62        Inquiry  concerning  the  Nature  of  Heat, 

The  thermoscope  was  laid  down  on  one  side,  so  that 
the  two  ends  of  its  tube,  to  which  its  balls  were  attached, 
instead  of  being  vertical,  were  now  in  a  horizontal  posi- 
tion ;  and  the  cold  body,  instead  of  being  presented 
to  the  ball  of  the  instrument  on  one  side  of  it,  and  on 
the  same  horizontal  level  with  it,  was  now  placed  di- 
rectly under  if,  and  at  the  distance  of  6  inches. 

This  cold  body,  instead  of  being  a  metallic  substance, 
was  a  solid  cake  of  ice,  circular,  flat,  and  about  3  inches 
thick,  and  8  inches  in  diameter.  It  was  placed  in  a 
shallow  earthen  dish,  about  9  inches  in  diameter  below, 
12  inches  in  diameter  above,  at  its  brim,  and  4  inches 
deep.  The  cake  of  ice  being  laid  down  on  the  bottom 
of  the  dish,  the  top  of  the  dish  was  covered  by  a  circu- 
lar piece  of  thick  paper,  14  inches  in  diameter,  which 
had  a  circular  hole  in  its  centre,  just  6  inches  in  di- 
ameter. 

This  earthen  dish,  containing  the  ice,  and  thus  cov- 
ered, was  placed  perpendicularly  under  one  of  the  balls 
of  the  thermoscope,  at  such  a  distance  that  the  centre 
of  the  upper  surface  of  the  flat  cake  of  ice  was  6  inches 
below  the  ball. 

The  result  of  this  experiment  was  just  what  might 
have  been  expected :  the  ice  was  no  sooner  placed  under 
the  ball  of  the  instrument  than  the  bubble  of  spirit  of 
wine  began  to  move  towards  that  side  where  the  cold 
body  was  placed ;  and  it  did  not  remain  stationary  till 
after  it  had  advanced  more  than  an  inch  in  the  tube. 

Experiment  No.  19. —  Desirous  of  discovering  whether 

,  the  surface  of  a  liquid  emits  frigorific  or  calorific  rays, 

as  solid  bodies  have  been  found  to  do,  I  now  removed 

the  cake  of  ice  from  the  earthen  dish,  and  replaced  it 

with  an  equal  mass  of  ice-cold  water. 


and  the  Mode  of  its  Communication.  63 

The  result  of  this  experiment  was,  to  all  appearance, 
just  the  same  as  that  of  the  last.  The  bubble  moved 
towards  the  cold  body,  and  took  its  station  in  the  same 
place  where  it  had  remained  stationary  before.  I  found 
reason,  however,  to  conclude,  after  meditating  on  the 
subject,  that  although  the  last  experiment  proves,  in  a 
most  decisive  manner,  that  radiations  actually  proceed 
from  the  surface  of  water^  yet  the  proof  of  the  radiation 
from  the  surface  of  ice,  afforded  by  the  preceding  ex- 
periment, is  not  equally  conclusive ;  for,  as  the  tem- 
perature of  the  air  of  the  room  in  which  these  experi- 
ments were  made  was  many  degrees  above  the  freezing 
point,  it  is  possible,  and  even  probable,  that  the  surface 
of  the  ice  was  actually  covered  with  a  very  thin,  and 
consequently  invisible,  coating  of  water  during  the 
whole  of  the  time  the  experiment  lasted. 

Finding  reason  to  conclude  that  frigorific  rays  are 
always  emitted  by  cold  bodies,  and  that  these  emana- 
tions are  very  analogous  to  the  calorific  rays  which  hot 
bodies  emit,  I  was  impatient  to  discover  whether  all 
cold  bodies,  at  the  same  temperature,  emit  the  same 
quantity  of  rays,  or  whether  (as  I  had  found  to  be  the 
case  with  respect  to  the  calorific  rays  emitted  by  hot 
bodies)  some  substances  emit  more  of  them  and  some 
less. 

With  a  view  to  the  ascertaining  of  this  important 
point,  I  made  the  following  experiments. 

Experiment  No.  20.  —  Having  found  that  a  metallic 
surface,  rendered  quite  black  by  holding  it  over  the 
flame  of  a  wax  candle,  emits  a  much  larger  quantity  of 
calorific  rays  when  hot,  than  the  same  metal,  at  the 
same  temperature,  throws  ofF  when  naked,  I  was  very 
curious  to  find  out  whether  blackening  the  surface  of 


64        Inquiry  concerning  the  Natiire  of 

a  cold  metal  would  or  would  not  increase,  in  like  man- 
ner, the  quantity  of  frigorific  rays  emitted  by  it. 

Having  blackened,  in  the  manner  already  described, 
the  flat  bottom,  or  rather  end,  of  one  of  my  horizontal 
cylindrical  brass  vessels  with  an  oblique  neck,  I  rilled  it 
with  a  mixture  of  ice  and  common  salt ;  and,  filling 
another  vessel  of  the  same  kind,  the  bottom  of  which 
was  not  blackened,  with  the  same  cold  mixture,  I  pre- 
sented them  both,  at  the  same  instant,  and  at  the  same 
distance,  to  the  two  opposite  balls  of  my  thermoscope. 

The  result  of  this  experiment  was  perfectly  conclu- 
sive :  the  bubble  of  spirit  of  wine  began  immediately  to 
move  towards  the  ball  to  which  the  blackened  cold  body 
was  presented  ;  indicating  thereby  that  that  ball  was 
more  cooled  by  the  frigorific  rays  which  proceeded  from 
the  blackened  surface  than  the  opposite  ball  was  cooled 
by  the  rays  which  proceeded  from  an  equal  surface  of 
naked  metal,  at  the  same  temperature. 

As  this  experiment  appeared  to  me  to  be  of  great 
importance,  I  repeated  it  several  times,  and  always  with 
the  same  results ;  the  motion  of  the  bubble,  which  con- 
stituted the  index  of  the  instrument,  constantly  show- 
ing that  the  frigorific  rays  from  the  blackened  surface 
were  more  powerful  in  generating  cold  than  those 
which  proceeded  from  the  naked  metal. 

The  bubble,  it  is  true,  did  not  move  so  far  out  of  its 
place  as  it  had  done  in  the  experiments  in  which  hot 
bodies  were  presented  to  the  balls ;  but  this  was  not  to 
be  expected,  for  though  I  had  taken  pains,  by  mixing 
salt  with  the  ice,  to  produce  as  great  a  degree  of  cold  as 
I  conveniently  could,  yet  still  the  difference  between 
the  temperature  of  the  balls  and  that  of  the  bodies  pre- 
sented to  them  was  much  greater  when  the  hot  bodies 


and  the  Mode  of  its  Communication.  65 

were  used  than  when  the  experiments  were  made  with 
the  cold  bodies  ;  and  it  is  evident,  that  the  distance  to 
which  the  bubble  is  driven  out  of  its  place  must  neces- 
sarily be  greater  or  less  in  proportion  as  that  difference 
is  greater  or  less. 

In  those  experiments  in  which  the  horizontal  cylin- 
drical vessels  were  filled  with  hot  water,  and  then  pre- 
sented to  the  balls  of  the  instrument,  the  temperature 
of  the  circular  flat  surfaces  was  that  of  180°,  while  the 
temperature  of  the  air  of  the  room  in  which  those  ex- 
periments were  made,  and  consequently  that  of  the 
balls,  was  about  60°;  the  difference  amounts  to  no  less 
than  1 20  degrees  of  Fahrenheit's  scale;  but,  in  these 
experiments  with  cold,  the  difference  of  the  tempera- 
tures at  the  moment  when  the  cold  bodies  were  first 
presented  to  the  instrument  did  not  probably  amount 
to  more  than  40,  or  at  the  most  50  degrees;  and  in  a 
very  few  seconds  it  must  have  been  reduced  to  less 
than  30  degrees,  in  consequence  of  the  freezing  of 
the  water  precipitated  by  the  air  of  the  atmosphere 
on  the  surface  of  the  vessel  containing  the  cold  mixt- 
ure. 

This  precipitation  of  water  by  the  surrounding  air 
was  so  copious  that  the  brilliancy  of  the  polish  of  the 
metallic  surface  was  almost  instantly  obscured  by  it, 
and  the  vessels  were  very  soon  covered  with  a  thick 
coat  of  ice.  These  accidents,  which  were  not  to  be 
prevented,  affected  in  a  very  sensible  manner  the  results 
of  the  experiment.  The  bubble,  instead  of  remaining 
stationary  for  some  time  after  it  had  reached  the  point 
of  its  greatest  elongation,  as  it  had  done  in  the  experi- 
ments with  hot  bodies,  had  no  sooner  reached  that 
point  than  it  began  to  return  back  towards  the  place 
VOL.  ii.  5 


66        Inquiry  concerning  the  Nature  of  Heat, 

from  which  it  had  set  out ;  and,  as  often  as  I  wiped  off 
the  ice  from  the  surface  of  the  flat  end  of  the  vessel 
which  was  not  blackened,  and  presented  it  clean  and 
bright  to  the  ball  of  the  instrument,  the  bubble  began 
again  to  move  towards  the  opposite  side,  —  which,  by 
the  bye,  shows  that  ice  emits  a  greater  quantity  of  frigo- 
rific  rays  than  a  bright  metallic  surface,  at  the  same 
temperature. 

Having  frequently  observed,  on  presenting  my  hand 
to  one  of  the  balls  of  the  thermoscope,  that  the  instru- 
ment was  greatly  affected  by  the  calorific  rays  which 
proceeded  from  it,  apparently  much  more  so  than  it 
would  have  been  by  a  much  hotter  body  of  the  same 
quantity  of  surface,  but  of  a  different  kind  of  substance, 
placed  at  the  same  distance,  I  was  extremely  curious  to 
find  out  whether  animal  substances  do  not  emit  calorific 
(and  consequently  frigorific)  rays  much  more  copiously 
than  other  substances,  and  whether  living  animal  bodies 
do  not  emit  them  in  greater  abundance  than  dead  ani- 
mal matter. 

The  first  experiment  I  made,  with  a  view  to  the 
investigation  of  this  particular  point,  was  as  simple  as 
its  result  was  striking  and  conclusive. 

Experiment  No.  21. —  Having  procured  a  piece  of 
gold-beater's  skin  (which,  as  is  well  known,  is  one  of 
the  membranes  that  line  the  larger  intestines  in  cattle, 
and  is  exceedingly  thin),  I  moistened  it  with  water;  and, 
applying  it,  while  moist,  to  the  flat  circular  end  of  one 
of  my  horizontal  cylindrical  vessels,  it  remained  firmly 
attached  to  the  surface  of  the  metal  when  it  became 
dry.  I  now  filled  this  vessel,  and  another,  of  equal 
dimensions,  the  end  of  which  was  not  covered,  with 
hot  water  (at  the  temperature  of  180°),  and  presented 


and  the  Mode  of  its  Communication.  67 

them  both,  at  the  same  moment,  to  the  two  balls  of  the 
thermoscope,  and  at  the  same  distance. 

The  bubble  of  spirit  of  wine  was  immediately  driven 
out  of  its  place  to  a  great  distance;  and  did  not  return 
to  its  former  station  till  after  the  vessel  whose  end  was 
covered  with  gold-beater's  skin  had  been  removed  to  a 
distance  from  the  ball  to  which  it  was  presented  which 
was  five  times  greater  than  the  distance  at  which  the 
other  vessel  was  placed  from  the  opposite  ball. 

I  was  induced  to  conclude,  from  the  result  of  this 
interesting  experiment,  that  an  animal  substance  emits 
25  times  more  calorific  rays  than  a  polished  metallic  sur- 
face of  the  same  dimensions,  both  substances  being  at 
the  same  temperature. 

Experiment  No.  22.  —  Having  emptied  both  the  ves- 
sels used  in  the  last  experiment,  and  refilled  them  with 
pounded  ice  and  water,  I  now  presented  them  again  to 
the  thermoscope,  at  equal  distances  from  their  respec- 
tive balls. 

The  result  of  this  experiment  confirmed  the  conclu- 
sion I  had  been  induced  to  draw  from  a  former  experi- 
ment of  the  same  kind  (No.  13),  the  motion  of  the 
bubble  towards  the  vessel  whose  surface  was  covered 
with  gold-beater's  skin  showing  that  the  rays  which 
proceeded  from  that  animal  substance  were  considerably 
more  efficacious  in  producing  cold  than  those  which 
proceeded  from  the  naked  metal. 

The  radiation  of  cold  bodies  appearing  to  me  to  have 
been  proved  beyond  all  doubt  by  the  preceding  experi- 
ments, I  now  set  about  to  investigate  a  very  important 
point  which  still  remained  to  be  determined :  I  en- 
deavoured to  find  out  whether  the  intensity  of  the 
action  of  the  frigorific  rays  which  proceed  from  cold 


68        Inquiry  concerning  the  Natzire  of  Heat, 

bodies,  or  their  power  of  affecting  the  temperatures  of 
other  warmer  bodies,  at  equal  intervals  of  temperature^  is, 
or  is  not,  equal  to  .the  intensity  of  the  action  of  the 
calorific  rays  which  proceed  from  hot  bodies.  To  as- 
certain this  point,  I  made  the  following  very  simple 
and  decisive  experiment. 

Experiment  No.  23. —  Having  placed  the  thermoscope 
on  a  table,  in  the  middle  of  a  large  quiet  room,  at  the 
temperature  of  72°  F.,  I  presented  to  one  of  its  balls,  at 
the  distance  of  3  inches,  the  flat  circular  end  of  one  of 
the  horizontal  cylindrical  vessels  (A)  above  described, 
with  an  oblique  cylindrical  neck,  this  vessel  being  filled 
with  pounded  ice  and  water ;  and,  at  the  same  moment, 
an  assistant  presented  to  the  opposite  side  of  the  same 
ball  of  the  thermoscope,  at  the  same  distance  (3  inches), 
the  flat  end  of  the  other  similar  and  equal  cylindrical 
vessel  (B),  filled  with  warm  water  at  the  temperature 
of  112°  F.,  the  opposite  ball  of  the  thermoscope  being 
hid  and  defended,  by  means  of  screens,  from  the  actions 
of  the  bodies  presented  to  the  other  ball,  as  also  from 
the  calorific  rays  which  proceeded  from  the  bodies  of 
the  persons  present. 

From  this  description  it  appears,  that  while  one  of 
the  balls  of  the  thermoscope  was  so  defended  by  screens 
that  it  could  not  be  sensibly  affected  by  the  radiations 
of  the  neighbouring  bodies,  the  other  ball  was  exposed 
to  the  simultaneous  action  of  two  equal  bodies,  at  equal 
distances  (two  vertical  metallic  disks,  3  inches  in  di- 
ameter, placed  on  opposite  sides  of  the  ball,  at  the 
distance  of  3  inches)  ;  one  of  these  bodies  being  at  the 
temperature  of  32°  F.,  or  40  degrees  below  that  of  the 
ball,  while  the  other  was  at  112°  F.,  or  40  degrees 
above  the  temperature  of  the  ball. 


and  the  Mode  of  its  Communication.  69 

I  knew,  from  the  results  of  former  experiments,  that 
this  ball  would,  at  the  same  time,  be  heated  by  the  calo- 
rific rays  from  the  hot  body  and  cooled  by  the  frigo- 
rific  rays  from  the  cold  body  ;  and  I  concluded  that  if 
its  mean  temperature  should  remain  unchanged  under 
the  influence  of  these  two  opposite  actions,  that  event 
would  be  a  decisive  proof  of  the  equality  of  the  inten- 
sities of  those  actions. 

The  result  of  the  experiment  showed  that  the  inten- 
sities of  those  opposite  actions  were  in  fact  equal ;  the 
bubble  of  spirit  of  wine,  which,  by  its  motion,  would 
have  indicated  the  smallest  change  of  temperature  in 
the  ball  of  the  thermoscope  to  which  the  hot  and 
the  cold  bodies  were  presented,  remained  at  rest. 

On  removing  the  cold  body  a  little  farther  from  the 
ball,  —  to  the  distance  of  3}  inches,  for  instance,  —  the 
hot  body  remaining  in  its  former  station,  at  the  distance 
of  3  inches,  the  bubble  began  immediately  to  move  to- 
wards the  opposite  ball  of  the  thermoscope,  indicating 
an  increase  of  heat  in  the  ball  exposed  to  the  actions  of 
the  hot  and  the  cold  bodies  ;  but,  when  the  hot  body 
was  removed  to  a  greater  distance,  the  cold  body  re- 
maining in  its  place,  the  bubble  indicated  an  increase  of 
cold. 

The  celerity  with  which  the  ball  of  the  thermoscope 
acquired  heat  or  cold  might  be  estimated  by  the  ve- 
locity with  which  the  bubble  of  spirit  of  wine  advanced 
or  retired  in  its  tube ;  but,  on  the  most  careful  and 
attentive  observation,  I  could  not  perceive  that  it 
moved  faster  when  the  ball  was  acquiring  heat  than 
when  it  was  acquiring  cold,  provided  that  the  hot  and 
the  cold  bodies  from  which  the  calorific  and  frigorific 
rays  proceeded  were  at  the  same  relative  distances. 


70         Inquiry  concerning  the  Natiire  of  Heat, 

From  these  experiments,  which  I  lately  repeated  at 
Geneva,  in  the  presence  of  Professor  Pictet,  Mons.  de 
Saussure,  M.  Senebier,  and  several  other  persons,  we 
may  venture  to  conclude,  that,  at  equal  intervals  of  tem- 
perature, the  rays  which  generate  cold  are  just  as  real, 
and  just  as  intense,  as  those  which  generate  heat ;  or, 
that  their  actions  are  equally  powerful  in  changing  the 
temperatures  of  neighbouring  bodies. 

On  a  superficial  view  of  this  subject,  it  might  appear 
extraordinary  that  so  important  a  fact  as  that  of  the 
frigorific  radiations  of  cold  bodies  should  have  been  so 
long  unnoticed,  while  the  calorific  radiations  of  hot 
bodies  have  been  so  well  known ;  but,  if  we  consider 
the  matter  with  attention,  our  surprise  will  cease. 
Those  radiations  by  means  of  which  the  temperatures 
of  neighbouring  bodies  are  gradually  changed  and  equal- 
ized are  not  sensible  to  our  feeling  unless  the  intervals 
of  temperature  be  very  considerable ;  and  the  constitu- 
tion of  things  is  such,  that,  while  we  are  often  exposed 
to  the  influence  of  bodies  heated  several  thousand  de- 
grees (as  measured  by  the  thermometer)  above  the 
mean  temperature  of  the  surface  of  the  skin,  it  is  very 
seldom  that  we  have  opportunities  of  experiencing  the 
effects  of  the  radiations  of  bodies  much  colder  than 
ourselves,  and  we  have  no  means  of  producing  degrees 
of  cold  which  bear  any  proportion  to  the  intense  heats 
excited  by  means  of  fire. 

From  the  result  of  the  experiment  of  which  an  ac- 
count has  just  been  given,  it  is  evident  that  we  should 
be  just  as  much  affected  by  the  calorific  rays  emitted  by 
a  cannon  bullet  at  the  temperature  of  160  degrees  of 
Fahrenheit's  scale  (=  64  degrees  above  that  of  the 
blood)  as  by  the  frigorific  rays  of  an  equal  bullet,  ice 


and  the  Mode  of  its  Communication.  7 1 

cold,  placed  at  the  same  distance ;  and  that  a  bullet  at 
the  temperature  of  freezing  mercury  could  not  affect  us 
much  more  sensibly,  by  its  frigorific  rays,  than  an  equal 
bullet  at  the  temperature  of  boiling  water  would  do 
by  its  calorific  rays  ;  —  but  at  these  comparatively  small 
intervals  of  temperature,  the  radiations  of  bodies  are 
hardly  sensible,  and  could  never  have  been  perceived, 
much  less  compared  and  estimated,  without  the  assist- 
ance of  instruments  much  more  delicate  than  our  or- 
gans of  feeling.  Hence  we  see  how  it  happened  that 
the  frigorific  radiations  of  cold  bodies  remained  so  long 
unknown.  They  were  suspected  by  Bacon  ;  but  their 
existence  was  first  ascertained  by  an  experiment  made 
at  Florence  towards  the  end  of  the  seventeenth  century. 
And  it  is  not  a  little  curious,  that  the  learned  academi- 
cians who  made  that  experiment,  and  who  made  it  with 
a  direct  view  to  determine  the  fact  in  question,  were  so 
completely  blinded  by  their  prejudices  respecting  the 
nature  of  heat  that  they  did  not  believe  the  report  of 
their  own  eyes  ;  but,  regarding  the  reflection  and  con- 
centration of  cold  (which  they  considered  as  a  negative 
quality)  as  impossible^  they  concluded  that  the  indica- 
tion of  such  reflection  and  concentration  which  they 
observed  must  necessarily  have  arisen  from  some  error 
committed  in  making  the  experiment. 

Happily  for  the  progress  of  science,  the  matter  was 
again  taken  up,  about  twenty  years  ago,  by  Professor 
Pictet ;  and  the  interesting  fact,  which  the  Florentine 
academicians  would  not  discover,  was  put  beyond  all 
doubt.  But  still,  this  ingenious  and  enlightened  phi- 
losopher did  not  consider  the  appearances  of  a  reflection 
of  cold,  which  he  observed  in  his  experiments,  as  being 
real;  nor  was  he  led  by  them  to  admit  the  existence  of 


72        Inquiry  concerning  the  N attire  of  Heat, 

frigorific  emanations  from  cold  bodies,  analogous  to 
those  calorific  emanations  from  hot  bodies  which  he 
calls  radiant  heat.  He  everywhere  speaks  of  the  reflec- 
tion of  cold  (by  metallic  mirrors)  as  being  merely  appar- 
ent ;  and  it  is  on  that  supposition  that  the  explanation 
he  has  given  of  the  phenomena  is  founded. 

On  a  supposition  that  the  caloric  of  modern  chemists 
has  any  real  existence,  and  that  heat,  or  an  increase  of 
temperature  in  any  body,  is  caused  by  an  accumulation 
of  that  substance  in  such  body,  the  reflection  of  cold 
would  indeed  be  impossible ;  and  the  supposition  that 
such  an  event  had  taken  place  would  be  absurd,  and 
could  not  be  admitted,  however  striking  and  convincing 
the  appearances  might  be  which  indicated  that  event. 
But,  to  return  from  this  digression  :  — 

Having  found  that  the  intensity  of  the  calorific  rays 
emitted  by  a  hot  body,  at  any  given  temperature,  de- 
pends much  on  the  surface  of  such  body,  —  that  a  pol- 
ished metallic  surface,  for  instance,  throws  off  much 
fewer  rays  than  the  same  surface,  at  the  same  tempera- 
ture, would  emit  if  painted,  or  blackened  in  the  smoke 
of  a  lamp  or  candle,  —  I  was  desirous  of  finding  out 
whether  the  frigorific  rays  from  cold  bodies  are  affected 
in  the  same  manner,  by  the  same  means,  and  in  the 
same  degree. 

It  was  to  ascertain  that  point  that  the  experiment 
No.  20  was  made ;  and  although  the  result  of  that  ex- 
periment afforded  abundant  reason  to  conclude  that 
those  substances  which,  when  hot,  throw  off  calorific 
rays  in  the  greatest  abundance,  actually  throw  off  great 
quantities  of  frigorific  rays  when  they  are  cold,  yet,  as 
the  relative  quantities  of  these  rays  could,  not  be  ex- 
actly determined  by  that  experiment,  in  order  to  ascer- 


and  the  Mode  of  its  Communication.  73 

tain  so  important  a  fact  I  had  recourse  to  the  following 
simple  contrivance. 

Experiment  No.  24. —  Having  found,  by  the  result 
of  the  last  experiment  (No.  23),  that  the  calorific  ema- 
nations of  a  circular  disk  of  polished  brass,  3  inches  in 
diameter,  at  the  temperature  of  112°  F.,  were  just 
counterbalanced  by  the  frigorific  emanations  of  an  equal 
disk  of  the  same  polished  metal,  at  the  temperature  of 
32°  F.,  placed  opposite  to  it,  so  that  one  of  the  balls  of 
the  thermoscope  placed  between  these  two  disks,  at 
equal  distances,  was  just  as  much  heated  by  the  one  as 
it  was  cooled  by  the  other,  I  now  blackened  the  two 
disks,  by  holding  them  over  the  flame  of  a  wax  candle, 
and  repeated  the  experiment  with  them  so  blackened. 

I  knew,  from  the  results  of  former  experiments,  that 
the  intensity  of  the  calorific  radiations  from  the  hot 
disk  would  be  very  much  increased,  in  consequence  of 
its  surface  being  blackened ;  and  I  was  certain  that,  if 
the  intensity  of  the  frigorific  radiations  of  the  cold  disk 
should  not  be  increased  in  exactly  the  same  degree,  the 
ball  of  the  thermoscope,  exposed  to  the  simultaneous 
actions  of  these  two  disks,  could  not  possibly  remain  at 
the  same  constant  temperature,  that  of  72°. 

The  result  of  the  experiment  was  very  decisive  ;  the 
bubble  of  spirit  of  wine  remained  at  rest,  — which  proved 
that  the  intensities  of  the  rays  emitted  by  the  two  disks 
still  continued  to  be  equal  at  the  surface  of  the  ball 
of  the  thermoscope,  which,  at  equal  distances,  was  ex- 
posed to  their  simultaneous  action. 

Hence  we  may  conclude,  that  those  circumstances 
which  are  favourable  to  the  copious  emission  of  calorific 
rays  from  the  surfaces  of  hot  bodies  are  equally  favour- 
able to  a  copious  emission  of  frigorific  rays  from  similar 
bodies  when  they  are  cold. 


74        Inquiry  concerning  tlie  Nature  of  Heat, 

But  it  is  time  to  consider  these  emanations  in  a  new 
point  of  view.  What  difference  can  there  be  between 
calorific  rays  and  frigorific  rays  ?  Are  not  the  same 
rays  either  calorific  or  frigorific  according  as  the  body  at 
whose  surface  they  arrive  is  hotter  or  colder  than  that 
from  which  they  proceed  ? 

Let  us  suppose  three  equal  bodies,  A,  B,  and  C, 
(the  globular  bulbs  of  three  mercurial  thermometers, 
for  instance,)  to  be  placed  at  equal  distances  (3  inches) 
in  the  same  horizontal  line ;  and  let  A  be  at  the  tem- 
perature of  freezing  water,  B  at  the  temperature  of  72° 
F.,  and  C  at  that  of  102°  F.  The  rays  emitted  by  B 
will  be  calorific  in  regard  to  the  colder  body  A,  but  in 
respect  to  the  hotter  body  C  they  will  be  frigorific; 
and,  from  the  results  of  the  two  last  experiments,  we 
have  abundant  reason  to  conclude  that  they  will  be 
just  as  efficacious  in  heating  the  former  as  in  cooling 
the  latter. 

Before  I  proceed  to  give  an  account  of  the  experi- 
ments which  were  made  with  a  view  to  determine  the 
relative  quantities  of  rays  emitted  from  the  surfaces  of 
various  substances,  from  living  animals,  dead  animal 
matter,  &c.  (which  I  must  reserve  for  a  future  com- 
munication), I  shall  lay  before  the  Society  the  results 
of  several  experiments,  of  various  kinds,  which  were 
made  with  a  view  to  the  farther  investigation  of  the 
radiations  of  hot  and  of  cold  bodies,  and  of  the  effects 
produced  by  them. 

Experiment  No.  25.  —  Having  found,  from  the  re- 
sults of  the  experiments  No.  21  and  No.  22,  that  great 
quantities  of  rays  are  thrown  off  from  the  surface  of  the 
animal  substance  used  in  those  experiments  (gold-beat- 
er's skin),  I  now  covered  the  whole  of  the  external  sur- 


and  the  Mode  of  its  Communication.  75 

face  of  one  of  my  large  cylindrical  passage  thermom- 
eters (No.  4)  with  that  substance  ;  and,  filling  it  with 
boiling-hot  water,  exposed  it  to  cool  gradually  in  the 
air  of  a  large  quiet  room,  in  the  manner  often  described 
in  former  parts  of  this  paper;  another  similar  naked 
standard  instrument  (No.  3  )  being  filled  with  hot  water  at 
the  same  time,  and  exposed  to  cool  in  the  same  situation. 
The  temperature  of  the  air  of  the  room  being  51  J°, 
the  instruments  were  found  to  cool  through  the  stand- 
ard interval  of  10  degrees,  namely,  from  IOI-J-  to  91^, 
in  the  following  times  :  — 

No.  4,  covered  \\\\k  gold-beater's  skin,      .      in  27!  minutes. 
No.  3,  which  was  naked,     ...  in  45  " 

Experiment  No.  16.  —  Being  desirous  of  finding  out 
whether  or  not  the  covering  of  animal  matter,  which 
had  so  remarkably  facilitated  the  cooling  of  the  instru- 
ment No.  4,  would  be  equally  efficacious  in  facilitating 
the  passage  of  heat  into  the  instrument,  I  suffered  both 
instruments  to  remain  in  the  cold  room  all  night  ;  and, 
entering  the  next  morning,  at  half  an  hour  past  seven 
o'clock,  I  found  the  temperature  of  the  water  in  the 
naked  instrument,  No.  3,  to  be  50^°;  that  in  the  instru- 
ment No.  4,  which  was  covered  with  gold-beater's  skin, 
was  49!"°  ;  while  the  air  of  the  room  was  at  48°. 

At  7  h.  30  m.  A.  M.  I  removed  both  instruments  into 
a  warm  room,  and  observed  the  times  of  their  acquiring 
heat  to  be  as  expressed  in  the  following  table. 


Observed  Temperature.  Temperature 

imes  when   the  obser-  No.  3,                                No.  4.                          of  the  air  of 

vations  were  made.  naked.                              covered,                          the  room. 

At  7  h.    30  rn.  .  .        50^°  .          .       49^°  .         .       64° 

7  45  -            5'i                       5»4           •           64* 

8  ..       .  .       5**  •        •       53*  '        •      6* 

8       15  •           531                      S4i 


j6        Inquiry  concerning  the  Nature  of  Heat, 

Observed  Temperature.  Temperature 

Times  when  the  obser-  No.  3,  No.  4,  of  the  air  of 

vations  were  made.  naked.  covered.  the  room. 

At  8h.  3011).   .         .       54$        .  56  ... 

8  45  •  55i  .  57i 

9  ...         ,       564       .         .       58£      .         ... 
93°          •  57^  •  60 

10  ...  .        58*  .         .      6i£  .         ... 

10  30  .  591-  .  62^ 

11  .  .       .•  .       6oJ  .        -63  .        ... 
ii  30          .            6 1                         63'  .          641 

The  results  of  this  experiment,  and  of  several  others 
similar  to  it,  showed,  in  a  manner  which  appeared  to 
me  to  be  perfectly  conclusive,  that  those  substances 
which  part  with  heat  with  the  greatest  facility,  or  celer- 
ity, are  those  which  also  acquire  it  most  readily,  or  with 
the  greatest  celerity. 

If  we  might  suppose  that  the  temperatures  of  bodies 
are  changed,  not  by  the  rays  they  emit,  but  by  those 
they  receive  from  other  neighbouring  bodies,  this  fact 
might  easily  be  explained ;  but,  without  stopping  to 
form  any  hypothesis  for  the  explanation  of  these  appear- 
ances, I  shall  proceed  in  my  account  of  the  various 
attempts  I  have  made  to  elucidate,  by  new  experiments, 
those  parts  of  this  interesting  subject  which  still  ap- 
peared to  be  enveloped  in  obscurity. 

As  the  cooling  of  hot  bodies  is  so  much  accelerated 
by  covering  their  surfaces  with  such  substances  as  emit 
calorific  rays  in  great  abundance,  or  with  such  as  are 
much  affected  by  the  frigorific  rays  of  the  colder  bodies 
by  which  they  are  surrounded,  it  seems  to  be  highly 
probable  that  a  comparatively  small  part  of  the  heat 
which  a  body  so  cooled  actually  loses  is  acquired  by 
the  air ;  a  much  greater  proportion  of  it  passing  off 
through  that  transparent  fluid,  under  the  form  of  calo- 
rific rays,  without  affecting  its  temperature. 


and  the  Mode  of  its  Communication.  77 

If  this  supposition  should  turn  out  to  be  well  founded, 
the  knowledge  of  the  fact  would  enable  us  to  explain 
several  interesting  phenomena,  and  particularly  that 
most  curious  process  by  means  of  which  living  animals 
preserve  an  equal  temperature,  notwithstanding  the  vast 
quantities  of  heat  that  are  continually  generated  in  the 
lungs,  and  notwithstanding  the  great  variations  which 
take  place  in  the  temperature  of  the  air  in  which  they 
live. 

It  is  evident,  that  the  greater  the  power  is  which  an 
animal  possesses  of  throwing  off  heat  from  the  surface 
of  his  body,  independently  of  that  which  the  surround- 
ing air  takes  off,  the  less  will  his  temperature  be  affected 
by  the  occasional  changes  of  temperature  which  take 
place  in  the  air,  and  the  less  will  he  be  oppressed  by 
the  intense  heats  of  hot  climates. 

It  is  well  known  that  negroes  and  people  of  colour 
support  the  heats  of  tropical  climates  much  better  than 
white  people.  Is  it  not  probable  that  their  colour  may 
enable  them  to  throw  off  calorific  rays  with  great  facil- 
ity, and  in  great  abundance ;  and  that  it  is  to  this  cir- 
cumstance they  owe  the  advantage  they  possess  over 
white  people  in  supporting  heat  ?  And,  even  should  it 
be  true,  that  bodies  are  cooled,  not  in  consequence  of 
the  rays  they  emit,  but  by  the  action  of  those  frigorific 
rays  they  receive  from  other  colder  bodies  (which  I 
•much  suspect  to  be  the  case),  yet,  as  it  has  been  found 
by  experiment  that  those  bodies  which  emit  calorific 
rays  in  the  greatest  abundance  are  also  most  affected  by 
the  frigorific  rays  of  colder  bodies,  it  is  evident  that  in 
a  very  hot  country,  where  the  air  and  all  other  sur- 
rounding bodies  are  but  very  little  colder  than  the  sur- 
face of  the  skin,  those  who  by  their  colour  are  prepared 


78         Inquiry  concerning  the  Nature  of  Heat, 

and  disposed  to  be  cooled  with  the  greatest  facility  will 
be  the  least  likely  to  be  oppressed  by  the  accumulation 
of  the  heat  generated  in  them  by  respiration,  or  of  that 
excited  by  the  sun's  rays. 

With  a  view  to  throw  some  light  on  this  interesting 
subject,  I  made  the  following  experiments. 

Experiment  No.  27.  —  Having  covered  the  flat  ends 
of  both  my  horizontal  cylindrical  vessels  with  gold- 
beater's skin,  I  painted  one  of  these  coverings  (of  this 
animal  substance)  black,  with  Indian  ink;  and  then, 
filling  both  vessels  with  boiling-hot  water,  I  presented 
them,  at  equal  distances,  to  the  two  opposite  balls '  of 
the  thermoscope. 

The  bubble  of  spirit  of  wine  was  immediately  driven 
out  of  its  place  by  the  superior  efficacy  of  the  calorific 
rays  which  proceeded  from  the  blackened  animal  sub- 
stance. 

On  repeating  this  experiment  a  great  number  of 
times,  and  when  the  water  in  the  vessels  was  at  different 
degrees  of  temperature  (the  temperature  being  the  same 
in  the  two  vessels  in  each  experiment),  the  results  uni- 
formly indicated  that  calorific  rays  were  thrown  off 
from  the  black  surface  in  greater  abundance  than  from 
the  equal  surface  which  was  not  blackened. 

Although  the  results  of  these  experiments  appeared 
to  me  to  be  so  perfectly  conclusive  as  to  establish  the 
fact  in  question  beyond  all  possibility  of  doubt,  yet,  in 
so  interesting  an  inquiry,  I  was  desirous,  by  varying 
my  experiments,  to  bring,  if  possible,  a  variety  of 
proofs  to  support  the  important  conclusions  which 
result  from  it. 

Experiment  No.  28. —  Having  covered  the  two  large 
cylindrical  vessels,  No.  3  and  No.  4,  with  gold-beater's 


and  the  Mode  of  its  Communication.  79 

skin,  I  painted  one  of  them  black,  with  Indian  ink; 
and,  filling  them  both  with  boiling-hot  water,  I  exposed 
them  to  cool,  in  the  manner  already  often  described,  in 
the  air  of  a  quiet  room. 

No.  4,  which  was  blackened,  cooled  through  the  stand- 
ard interval  of  10  degrees  in  23 1-  minutes;  while  the 
other,  No.  3,  which  was  not  blackened,  took  up  28 
minutes  in  cooling  through  the  same  interval. 

In  a  former  experiment  (No.  25),  the  instrument 
No.  4,  covered  with  gold-beater's  skin,  but  not  black- 
ened, had  taken  up  27!  minutes  in  cooling  through 
the  given  interval,  as  we  have  before  seen. 

The  results  of  these  experiments  do  not  stand  in 
need  of  illustration  ;  and  I  shall  leave  to  physicans  and 
physiologists  to  determine  what  advantages  may  be 
derived  from  a  knowledge  of  the  facts  they  establish, 
in  taking  measures  for  the  preservation  of  the  health  of 
Europeans  who  quit  their  native  climate  to  inhabit  hot 
countries. 

All  I  will  venture  to  say  on  the  subject  is,  that  were 
I  called  to  inhabit  a  very  hot  country,  nothing  should 
prevent  me  from  making  the  experiment  of  blackening 
my  skin,  or  at  least  of  wearing  a  black  shirt,  in  the 
shade,  and  especially  at  night ;  in  order  to  find  out  if, 
by  those  means,  I  could  not  contrive  to  make  myself 
more  comfortable. 

Several  of  the  savage  tribes  which  inhabit  very  cold 
countries  besmear  their  skins  with  oil,  which  gives 
them  a  shining  appearance.  The  rays  of  light  are  re- 
flected copiously  from  the  surface  of  their  bodies.  May 
not  the  frigorific  rays,  which  arrive  at  the  surface  of 
their  skin,  be  also  reflected  by  the  highly  polished  sur- 
face of  the  oil  with  which  it  is  covered  ? 


8o         Inquiry  concerning  the  Nature  of  Heat,, 

If  that  should  be  the  case,  instead  of  despising  these 
poor  creatures  for  their  attachment  to  a  useless  and 
loathsome  habit,  we  should  be  disposed  to  admire  their 
ingenuity,  or  rather  to  admire  and  adore  the  goodness 
of  their  invisible  Guardian  and  Instructor,  who  teaches 
them  to  like,  and  to  practise,  what  he  knows  to  be  use- 
ful to  them. 

The  Hottentots  besmear  themselves,  and  cover  their 
bodies,  in  a  manner  still  more  disgusting.  They  think 
themselves  fine,  when  they  are  besmeared  and  dressed 
out  according  to  the  loathsome  custom  of  their  country. 
But  who  knows  whether  they  may  not  in  fact  be  more 
comfortable,  and  better  able  to  support  the  excessive 
heats  to  which  they  are  exposed  ?  From  several  experi- 
ments which  I  made,  with  a  view  to  elucidate  that 
point,  (of  which  an  account  will  be  given  to  this  Soci- 
ety at  some  future  period,)  I  have  been  induced  to  con- 
clude that  the  Hottentots  derive  advantages  from  that 
practice  exactly  similar  to  those  which  negroes  derive 
from  their  black  colour. 

It  cannot  surely  be  supposed  that  I  could  ever  think 
of  recommending  seriously  to  polished  nations  the 
filthy  practices  of  these  savages.  That  is  very  far  in- 
deed from  being  my  intention,  for  I  have  ever  consid- 
ered cleanliness  as  being  so  indispensably  necessary  to 
comfort  and  happiness  that  we  can  have  no  real  enjoy- 
ment without  it ;  but  still  I  think  that  a  knowledge 
of  the  physical  advantages  which  those  savages  derive 
from  such  practices  may  enable  us  to  acquire  the  same 
advantages  by  employing  more  elegant  means.  A 
knowledge  of  the  manner  in  which  heat  and  cold  are 
excited  would  enable  us  to  take  measures  for  these 
important  purposes  with  perfect  certainty  ;  in  the  mean 


and  the  Mode  of  its  Communication.  81 

time,  we  may  derive  much  useful  information  by  a 
careful  examination  of  the  phenomena  which  occasion- 
ally fall  under  our  observation. 

If  it  be  true  that  the  black  colour  of  a  negro,  by 
rendering  him  more  sensible  to  the  few  frigorific  rays 
which  are  to  be  found  in  a  very  hot  country,  enables 
him  to  support  the  great  heats  of  tropical  climates  with- 
out inconvenience,  it  might  be  asked  how  it  happens 
that  he  is  able  to  support,  naked,  the  direct  rays  of  a 
burning  sun. 

Those  who  have  seen  negroes  exposed  naked  to  the 
sun's  rays,  in  hot  countries,  must  have  observed  that 
their  skins,  in  that  situation,  are  always  very  shining. 
An  oil  exudes  from  their  skin,  which  gives  it  that  shin- 
ing appearance ;  and  the  polished  surface  of  that  oil 
reflects  the  sun's  calorific  rays. 

If  the  heat  be  very  intense,  sweat  makes  its  appear- 
ance at  the  surface  of  the  skin.  This  watery  fluid  not 
only  reflects  very  powerfully  the  calorific  rays  from  the 
sun  which  fall  on  its  polished  surface,  but  also,  by  its 
evaporation,  generates  cold. 

When  the  sun  is  gone  down,  the  sweat  disappears  ; 
the  oil  at  the  surface  of  the  skin  retires  inwards ;  and 
the  skin  is  left  in  a  state  very  favourable  to  the  admis- 
sion of  those  feeble  frigorific  rays  which  arrive  from  the 
neighbouring  objects. 

But  I  shall  refrain  from  pursuing  these  speculations 
any  farther  at  present. 

I  shall  now  proceed  to  give  an  account  of  several  ex- 
periments, of  various  kinds,  which  were  made  with  a 
view  to  a  farther  investigation  of  the  radiations  of  cold 
bodies. 

Having  found,  by   several  of  the  foregoing  experi- 


82         Inquiry  concerning  the  Nature  of  Heat, 

ments,  that  the  radiations  of  cold  bodies  affected  my 
thermoscope  very  sensibly,  even  when  placed  at  a  con- 
siderable distance  from  it,  and  in  situations  where  cur- 
rents of  cold  air  could  not  be  suspected  to  exist,  I  was 
desirous  of  rinding  out  whether  the  cooling  of  a  hot 
body  would  or  would  not  be  sensibly  accelerated  by 
those  rays.  To  determine  that  point,  I  made  the  fol- 
lowing experiment. 

Experiment  No.  29. —  Having  provided  two  conical 
vessels,  made  of  thin  sheet  brass,  each  4  inches  in  diam- 
eter at  the  base,  and  4  inches  high,  ending  above  in  a 
cylindrical  neck,  0.88  of  an  inch  in  diameter,  I  enclosed 
each  of  them  in  a  cylinder  of  thin  pasteboard,  covered 
with  gilt  paper,  and  then  covered  them  up  with  rabbit- 
skins,  which  had  the  hair  on  them,  in  such  a  manner  that 
no  part  of  these  vessels,  except  their  flat  bottoms,  was 
exposed  naked  to  the  air.  I  then  covered  their  bottoms 
with  gold-beater's  skin,  painted  black  with  Indian  ink, 
in  order  to  render  them  as  sensible  as  possible  to  calo- 
rific and  frigorific  rays. 

This  being  done,  I  suspended  these  two  vessels  in 
an  erect  position,  or  with  their  bottoms  downwards,  to 
the  two  opposite  horizontal  arms  of  a  wooden  stand, 
provided  for  the  experiment;  and  I  placed  under  each 
of  them  a  pewter  platter,  blackened  on  the  inside  by 
holding  it  over  a  lighted  wax  candle. 

Each  of  these  platters  was  12  inches  in  diameter, 
and  they  were  supported  on  the  top  of  two  shallow 
earthen  dishes,  each  of  which  was  1 1^  inches  in  diameter 
at  its  brim  ;  these  earthen  dishes  being  supported  on 
circular  wooden  stands  10  inches  in  diameter. 

A  circular  piece  of  thick  drawing-paper,  i2|  inches 
in  diameter,  with  a  circular  hole  in  its  centre,  just  6 


and  the  Mode  of  its  Communication.  83 

inches  in  diameter,  was  placed  on  each  of  the  platters, 
and  served  as  a  perforated  cover  to  it. 

The  stands  on  which  the  platters  were  supported 
were  of  such  a  height  that  the  upper  surface  of  the  flat 
bottom  of  each  of  the  platters  was  elevated  just  40 
inches  above  the  level  of  the  floor  of  the  room ;  and 
the  horizontal  arms  of  the  wooden  stand  which  sup- 
ported the  conical  vessels  were  of  such  a  height  that 
the  flat  bottoms  of  these  vessels  (which  were  placed  per- 
pendicularly over  the  centres  of  the  platters)  were  just 
4  inches  above  the  flat  horizontal  surface  of  the  bottoms 
of  the  platters. 

One  of  the  platters  was  at  the  temperature  of  the  air 
of  the  room  (63°  F.),  but  the  other  was  kept  constantly 
ice-cold,  during  the  whole  of  the  time  the  experiment 
lasted,  by  means  of  pounded  ice  and  water,  which  was 
put  into  the  earthen  dish,  over  which,  or  rather  in 
which,  this  platter  was  placed. 

Each  of  the  platters  was  just  I  inch  deep,  measured 
from  the  level  of  the  top  of  its  brim  to  the  level  of  the 
upper  surface  of  the  flat  part  of  its  bottom ;  this  flat 
part  was  about  8  inches  in  diameter. 

The  £wo  conical  vessels  were  now  filled  with  boiling- 
hot  water,  and  the  times  of  their  cooling  were  carefully 
observed. 

From  the  above  description  of  the  apparatus  used  in 
this  experiment,  it  is  evident  that  the  vessel  which  was 
suspended  over  the  ice  could  not  be  reached  by  any 
streams  of  cold  air  that  might  be  occasioned  by  that  ice, 
or  by  the  cooled  sides  of  the  vessel  which  contained 
it ;  for  the  air  which,  coming  into  contact  with  the  sides 
of  that  vessel,  was  cooled  by  it,  becoming  specifically 
heavier  than  it  was  before,  naturally  descended,  and 


84        Inquiry  concerning  the  Natiire  of  Heat, 

spread  itself  out  on  the  floor  of  the  room  ;  and  the  per- 
forated circular  sheet  of  paper,  which  was  laid  down 
horizontally  on  the  platter,  effectually  prevented  any  of 
the  air  so  cooled  from  being  thrown  upwards  against 
the  bottom  of  the  conical  vessel  (placed  immediately 
over  the  platter),  by  any  occasional  undulation  of  the  air 
in  the  room. 

To  preserve  the  air  of  the  room  in  a  state  of  perfect 
quietness,  not  only  the  doors  and  windows,  but  even 
the  window-shutters  of  the  room  were  kept  shut ;  so 
much  light  only  being  admitted  occasionally  as  was 
necessary  to  observe  the  thermometers  which  were 
placed  in  the  conical  vessels. 

In  order  to  guard  still  more  effectually  the  bottoms 
of  the  vessels  which  were  cooling  from  the  effects  of 
occasional  undulations  in  the  air  of  the  room,  over  each 
of  these  vessels  there  was  drawn  a  cylindrical  covering 
of  very  fine  thin  post  paper,  the  lower  open  end  of 
which  projected  just  half  an  inch  below  the  horizontal 
level  of  the  flat  bottom  of  the  vessel.  These  cylin- 
drical coverings  of  post  paper  were  made  to  fit  as  ex- 
actly as  possible  the  cylinders  of  pasteboard  by  which 
the  sides  of  the  conical  vessels  were  covered  and  de- 
fended from  the  air  ;  and  the  warm  coverings  of  fur 
(rabbit-skins)  were  put  over  all. 

To  confine  the  heat  still  more  effectually,  a  quantity 
of  eider-down  had  been  introduced  between  the  outside 
of  each  conical  vessel  and  its  cylindrical  neck,  and  the 
inside  of  the  hollow  cylinder  of  pasteboard  in  the  axis 
of  which  it  was  fixed  and  confined. 

The  result  of  this  experiment  was  very  conclusive. 
The  conical  vessel  which  was  suspended  over  the  ice- 
cold  pewter  platter  cooled  through  the  standard  interval 


and  the  Mode  of  its  Communication.  85 

of  10  degrees  (namely,  from  the  point  of  50  degrees  to 
that  of  40  degrees  above  the  temperature  of  the  air  of 
the  room)  in  33  minutes  and  42  seconds ;  whereas 
the  other  vessel,  which  was  not  over  ice,  required  39 
minutes  and  15  seconds  to  cool  through  the  same  in- 
terval. 

Experiment  No.  30.  —  On  repeating  this  experiment 
the  next  day,  the  air  of  the  room  still  remaining  at  63°, 
the  times  of  cooling  through  the  given  interval  were  as 
follows  :  — 

Min.  Sec. 

The  vessel  suspended  over  the  ice-cold  platter,  in     .     33    15 
The  other  vessel,  in 39  3° 

From  the  results  of  these  experiments  (which  were 
made  with  the  greatest  possible  care)  it  appears  that 
the  radiations  of  cold  bodies  act  on  warmer  bodies  at  a 
distance,  and  gradually  diminish  their  temperatures. 

It  will  likewise  be  evident,  when  we  consider  the 
matter  with  attention,  that  the  cooling  of  the  vessel 
which  was  suspended  over  the  ice-cold  platter  was  in 
fact  considerably  more  accelerated  by  the  frigorific  radia- 
tions from  that  cold  surface  than  it  appears  to  have 
been  when  we  estimate  the  effects  produced  simply  by 
the  difference  of  the  times  taken  up  in  the  cooling  of 
the  two  vessels,  without  having  regard  to  any  other 
circumstance. 

These  times  are,  no  doubt,  inversely  as  the  velocities 
of  cooling ;  but,  as  all  the  heat  lost  by  the  vessels  dur- 
ing the  time  of  their  cooling  did  not  pass  off  through 
their  flat  bottoms,  and  as  the  rays  from  the  cold  sur- 
face fell  on  the  bottom  only  of  the  vessel  which  was  sus- 
pended over  it,  without  at  all  affecting  its  covered  sides, 
the  velocity  with  which  the  heat  made  its  way  through 


86          Inquiry  concerning  the  Nature  of  Heat, 

the  covered  sides  of  the  vessels  was  the  same  in  both ; 
consequently,  more  heat  must  have  passed  that  way, 
and  of  course  less  through  the  bottom  of  the  vessel, 
when  the  time  of  cooling  was  the  longest,  that  is  to  say, 
in  the  vessel  which  was  not  p  aced  over  ice. 

As  the  cooling  of  these  vessels  is  a  complicated  pro- 
cess, I  will  endeavour  to  elucidate  the  subject  still 
farther. 

As  the  two  conical  vessels  were  of  the  same  form  and 
dimensions,  and  contained  equal  quantities  of  hot  water, 
the  quantities  of  heat  they  parted  with,  in  being  cooled 
the  same  number  of  degrees,  must  of  course  have  been 
equal. 

Expressing  that  quantity  by  the  algebraic  symbol  a, 
and  putting  x  =.  the  quantity  of  heat  which  passed  off 
through  the  covered  sides  of  the  vessel  which  was  sus- 
pended over  ice  during  the  time  it  was  cooling  through 
the  given  interval  of  10  degrees,  and  jy  =  the  quantity 
which  passed  off  through  the  covered  sides  of  the  other 
vessel  during  the  time  that  vessel  was  coo  ing  through 
the  same  interval,  the  quantity  of  heat  which  passed 
off  through  the  bottom  of  the  vessel  which  was  placed 
over  ice  during  the  time  it  was  cooling  through  the 
given  interval  must  have  been  =  a  —  x3  and  that 
which  passed  off  through  the  bottom  of  the  other  ves- 
sel during  the  time  of  its  cooling  through  the  same 
interval  =  a  — y. 

But,  as  the  velocities  of  the  heat  through  the  covered 
sides  of  both  vessels  must  have  been  equal,  the  quanti- 
ties of  heat  which  passed  off  that  way  must  have  been 
as  the  times  of  cooling. 

The  times  of  cooling  in  the  last-mentioned  experi- 
ment (No.  30)  were  as  follows  :  — 


and  the  Mode  of  its  Communication.  87 

Min.  Sec.        Seconds. 

Of  the  vessel  suspended  over  ice,       .         .     33    15=1995 
Of  the  other  vessel,       .         .         .         .         3930=2370 

x  is  therefore  tojy,  as   1995  to  2370;   consequently, 

x  =  '-Sr  =  0.841  77  y; 

And,  substituting  for  x  its  value  =  0.84177^,  the 
quantities  of  heat  which  passed  off  through  the  bottoms 
of  the  two  vessels,  in  the  experiment  in  question  (No. 
30),  must  have  been  =  a  —  0.84177  y  for  the  vessel 
which  was  suspended  over  ice,  and  =  a  — y  fort  he 
other  vessel. 

And,  asjy  is  greater  than  0.84177  jy,  consequently^  — 
0.84177  y  is  greater  than  a  — jy,  or  the  quantity  of  heat 
which  passed  off  through  the  bottom  of  the  vessel  which 
was  cooled  the  most  rapidly  was  greater  than  that 
which  passed  off  through  the  bottom  of  the  other  vessel ; 
and  hence  we  perceive  that  the  effect  produced  by  the 
frigorific  rays  from  the  cold  surface,  in  the  experiments 
in  question,  was  greater  than  it  appeared  to  be  at  first 
sight,  when  it  was  estimated  by  the  times  of  cooling. 

To  determine  exactly  how  much  the  cooling  was  ac- 
celerated by  the  presence  of  the  cold  body,  it  is  neces- 
sary to  find  out  how  much  heat  actually  passed  off 
through  the  bottoms  of  the  two  vessels,  in  the  experi- 
ments in  question.  This  we  will  endeavour  to  do  by 
comparing  the  results  of  those  experiments  with  the  re- 
sults of  some  other  experiments  of  a  similar  nature. 

In  the  experiment  No.  28,  a  cylindrical  vessel  of  thin 
sheet  brass,  4  inches  in  diameter,  and  4  inches  in  height, 
covered  with  gold-beater's  skin  painted  black  with  In- 
dian ink,  being  filled  with  hot  water  and  exposed  to 
cool  in  the  air  of  a  large  quiet  room,  cooled  from  the 
point  of  50  degrees  to  that  of  40  degrees  above  the 
temperature  of  the  air  of  the  room  in  23  \  minutes. 


88        Inquiry  concerning  the  Nature  of  Heat, 

The  quantity  of  surface  by  which  this  vessel  was  ex- 
posed to  the  cold  air  was  =  74.5581  superficial  inches, 
exclusive  of  its  neck,  which  was  well  covered  up  with 
fur. 

The  quantity  of  surface  which  was  exposed  to  the  air, 
in  the  foregoing  experiments  with  the  conical  vessels,  or 
the  area  of  the  bottom  of  each  of  the  vessels,  was  (4  X 
3.14159)  =  12.4263  superficial  inches. 

As  the  diameters  and  heights  of  the  conical  and  cylin- 
drical vessels  were  equal,  the  contents  of  the  former 
must  have  been  to  the  contents  of  the  latter  as  i  to  3  ; 
and  the  quantities  of  heat  which  they  lost  in  cooling 
were  .as  their  contents. 

If  now  the  cylindrical  vessel  lost  a  quantity  of  heat 
=  3  in  23^  minutes,  it  would  have  disposed  of  a 
quantity  =  I  (equal  to  that  which  the  conical  vessel 
lost)  in  one  third  part  of  that  time,  or  in  7  minutes 
and  50  seconds. 

But  the  quantity  of  surface  exposed  to  the  air  in  the 
experiment  with  the  cylindrical  vessel  was  to  that  so 
exposed  in  the  experiment  with  the  conical  vessel  as 
74.5581  to  12.4263,  or  as  6  to  i. 

Now,  as  the  time  in  which  any  given  quantity  of  heat 
can  pass  out  of  any  closed  vessel  into  or  through  any 
cold  fluid  medium  by  which  the  vessel  is  surrounded 
must  be  inversely  as  the  surface  of  the  vessel,  other 
things  being  equal,  if  a  quantity  of  heat  =  i  could 
pass  out  of  the  cylindrical  vessel  in  7  minutes  and  50 
seconds,  it  would  require  6  times  as  long,  or  47  min- 
utes, to  pass  out  of  the  conical  vessel  through  its  fiat 
bottom,  supposing  no  heat  whatever  to  escape  through 
the  covered  sides  of  that  vessel. 

If  now  the  whole  of  the  heat  which  the  conical  vessel 


and  the  Mode  of  its  Communication,  89 

actually  lost  would  have  required  47  minutes  to  have 
passed  through  the  bottom  of  that  vessel,  it  is  evident 
that  the  quantity  which  actually  passed  through  that 
surface,  in  the  experiment  in  question  (No.  30),  could 
not  have  been  to  the  whole  quantity  actually  lost  in  a 
greater  proportion  than  that  of  the  times,  or  as  39} 
to  47. 

Assuming  any  given  number  —  as  10,000,  for  instance 
—  to  represent  the  whole  of  the  heat  lost  in  the  experi- 
ment, we  can  now  determine  what  part  or  proportion 
of  it  passed  off  through  the  bottom  of  the  conical  ves- 
sel, and  consequently  how  much  of  it  must  have  made 
its  way  through  its  covered  sides. 

If  the  whole  quantity,  =  10,000,  would  have  re- 
quired 47  minutes  to  have  passed  through  the  bottom 
of  the  vessel,  the  quantity  which  actually  passed  through 
that  surface  in  39^  minutes  could  not  possibly  have 
amounted  to  more  than  8404,  =  a  — y. 

For  it  is  47  minutes  to  10,000,  as  39!  minutes  to 
8404.  The  remainder  of  the  heat,  =  10,000  —  8404 
=  1396  parts,  (=  y)  must  have  made  its  way  through 
the  covered  sides  of  the  vessel. 

And,  if  a  quantity  of  heat  =1396  required  397}  min- 
utes to  make  its  way  through  the  covered  sides  of  one 
of  the  conical  vessels,  the  quantity  which  made  its  way 
through  the  covered  sides  of  the  other  in  33 ' j-  minutes 
could  not  have  amounted  to  more  than  1175  parts ;  and 
the  remainder  of  that  which  was  actually  disposed  of  in 
the  experiment  =  10,000  —  n?5  —  8825  (=="  a  — 
#,)  must  have  passed  off  through  the  bottom  of  the  in- 
strument. 

Hence  it  appears,  that  the  quantity  of  heat  which 
actually  passed  off  through  the  bottom  of  the  conical 


90        Inquiry  concerning  the  Nature  of  Heat, 

vessel  which  was  placed  over  ice,  in  33^  minutes,  was 
to  that  which  passed  off  in  39^-  minutes  through  the 
bottom  of  the  other  vessel  as  8825  to  8404;  and  con- 
sequently, that  the  velocity  with  which  the  heat  passed 
through  the  bottom  of  the  vessel  which  was  exposed  to 
the  frigorific  rays  from  the  surface  of  the  cold  platter 
was  to  the  velocity  with  which  it  passed  through  the 
bottom  of  the  other  vessel  in  the  compound  ratio  of 
8825  to  8404,  and  of  39^  to  33^;  or  as  10,000  to 
8025,  which  is  as  5  to  4,  very  nearly. 

From  these  experiments  and  computations  it  appears 
that  the  cooling  of  the  hot  body  which  was  placed  over 
the  ice-cold  platter  was  sensibly,  and  very  consider- 
ably, accelerated  by  the  vicinity  of  that  cold  body,  — 
may  we  not  venture  to  say,  by  the  frigorific  rays  which 
proceeded  from  it  ? 

I  made  several  other  experiments  similar  to  those 
just  described,  and  with  similar  results ;  but  I  shall  not 
take  up  the  time  of  the  Society  by  giving  a  detailed 
account  of  them.  I  may,  perhaps,  at  a  future  time 
find  occasion  to  mention  some  of  them  more  particu- 
larly. 

In  the  two  last-mentioned  experiments,  as  the  conical 
vessels  were  suspended  in  an  erect  position,  and  had  a 
circular  band  or  hoop  of  fine  post  paper,  by  which  the 
lower  end  of  each  of  them  was  surrounded,  and  which 
projected  downwards  half  an  inch  below  the  horizontal 
level  of  the  bottom  of  the  vessel,  and  as  the  air  which 
came  into  immediate  contact  with  the  bottom  of  the 
vessel,  and  received  heat  from  it  (though  it  became 
specifically  lighter  than  it  was  before),  could  not  make 
its  escape  upwards  into  the  atmosphere,  being  confined 
and  prevented  from  moving  upwards  by  the  thin  pro- 


and  the  Mode  of  its  Communication.  91 

jecting  hoop  of  paper,  there  is  no  doubt  but  that  the 
time  of  cooling  was  prolonged  by  this  arrangement ; 
for,  there  being  much  reason  to  believe  that  the  propa- 
gation of  heat  downwards,  in  air,  from  one  particle  of 
that  fluid  to  another,  is  either  quite  impossible  or  so  ex- 
tremely slow  as  to  be  imperceptible,  as  a  succession  of 
fresh  particles  of  cold  air  was  prevented  from  coming 
into  contact  with  the  bottoms  of  the  vessels,  but  very 
little  heat  could  have  been  given  off  immediately  to  the 
air  in  those  experiments. 

In  order  to  be  able  to  form  some  probable  conjecture 
respecting  the  quantity  so  given  off  in  cases  where  the 
succession  of  fresh  particles  of  air  is  free  and  uninter- 
rupted, I  made  the  following  experiment. 

Experiment  No.  31. —  The  two  conical  vessels  used 
in  the  last  experiment  (which  I  shall  now  distinguish 
by  calling  the  one  No.  5  and  the  other  No.  6)  being 
left  suspended  in  the  air  to  the  two  horizontal  arms  of 
their  wooden  stand,  at  the  height  of  44  inches  above 
the  floor  of  the  room  (the  pewter  platters,  the  earthen 
dishes,  and  the  stands  on  which  they  were  placed  being 
removed),  both  the  vessels  were  again  filled  with  boiling 
hot  water,  and  exposed  to  cool  in  the  air. 

The  vessel  No.  5  remained  in  a  vertical  position,  or 
with  its  flat  bottom  in  a  horizontal  position,  as  before ; 
but  the  vessel  No.  6  was  now  reclined,  so  that  its  axis, 
and  consequently  the  plane  of  its  flat  bottom,  made  an 
angle  with  the  plane  of  the  horizon  of  45  degrees.  In 
this  position  of  the  vessel  No.  6,  it  is  evident  that  the 
air,  heated  by  coming  into  contact  with  its  bottom,  had 
full  liberty  to  escape  upwards,  and  to  make  way  for 
other  particles  of  colder  air  to  come  into  contact  with 
the  hot  surface  and  be  heated,  rarefied,  and  forced  up- 


92         Inquiry  concerning  the  Nature  of  Heat, 

wards  in  their  turns  ;  and  under  these  circumstances 
it  might  reasonably  be  expected  that  as  much  heat  as 
possible  would  be  communicated  immediately  to  the  air 
by  the  hot  body,  and  that  the  heat  so  communicated 
would  of  course  accelerate  the  cooling  of  that  vessel. 

It  was  in  fact  cooled  in  a  shorter  time  than  the  other, 
No.  5,  which  was  suspended  in  a  vertical  position  ;  but 
the  difference  of  the  times  of  cooling  was  very  small ; 
which  indicates,  if  I  am  not  mistaken,  that  a  compara- 
tively small  quantity  of  the  heat  a  hot  body  loses 
when  it  is  cooled  in  air  is  communicated  to  that  fluid, 
much  the  greater  part  of  it  being  sent  off  through  the 
air,  to  a  distance,  in  calorific  rays. 

The  vessel  No.  5  was  found  to  cool  through  the 
standard  interval  of  10  degrees  in  38-^  minutes;  and 
No.  6,  which  was  in  a  reclined  position,  in  37^  min- 
utes. 

It  will  no  doubt  be  remarked  that  the  vessel  No.  5 
cooled  somewhat  faster  in  this  experiment  than  it  had 
done  in  the  two  preceding  experiments  (No.  29  and 
No.  30),  when  it  stood  over  a  pewter  platter  which  (at 
the  beginning  of  the  experiment  at  least)  was  at  the 
same  temperature  as'  the  air  of  the  room. 

The  calorific  rays  from  the  bottom  of  the  vessel  heat- 
ing the  platter  in  some  small  degree,  and  still  more, 
perhaps,  the  upper  surface  of  the  perforated  sheet  of 
paper  which  covered  it,  the  frigorific  rays  from  these 
bodies  were,  on  that  account,  somewhat  less  powerful 
in  lowering  the  temperature  of  the  neighbouring  hot 
body  ;  and  the  time  of  its  cooling  was  consequently  a 
little  prolonged. 

In  one  of  the  preceding  experiments  it  cooled  through 
the  given  interval  in  39^-  minutes,  and  in  the  other  in 


and  the  Mode  of  its  Communication.  93 

minutes  ;  but  in  this  experiment  it  took  up  only 
38  J  minutes  in  cooling  through  it,  as  we  have  just  seen. 

Supposing  now  (what  appears  to  me  to  be  not  im- 
probable) that  all,  or  very  nearly  all,  the  heat  lost  by 
the  instrument  No.  5  passed  off  in  rays  through  the  air, 
we  can  ascertain  what  part  of  the  heat  lost  by  the  instru- 
ment No.  6  was  communicated  to  the  air  which  came 
into  contact  with  its  surface. 

Putting  the  total  quantity  of  heat  lost  by  each  of  the 
instruments  in  cooling  through  the  given  interval  = 
10,000,  as  we  have  just  seen  that  a  quantity  of  heat 
=  1396  passes  through  the  covered  sides  of  each  of 
these  instruments  in  39^-  minutes,  the  quantities  so  lost 
in  this  experiment  must  have  been  as  follows :  By 
the  instrument  No.  5,  in  38^  minutes,  =  1081  ;  by 
No.  6,  in  37  J  minutes,  =  1046  ;  and,  deducting  these 
quantities  so  lost  (through  the  covered  sides  of  the  in- 
struments) from  the  total  quantity  lost  by  each  (= 
10,000),  we  shall  find  out  how  much  heat  passed  off 
through  the  bottom  of  each  of  the  instruments. 

For  the  instrument  No.  5  it  is     .      10,000  —  1081  =  9919 
And  for         "         No.  6         .         10,000  —  1046  =  9954 

If  now  the  whole  of  the  heat  lost  through  the  bot- 
tom of  the  instrument  No.  5  passed  off  through  the  air 
in  rays,  as  there  is  no  reason  to  suppose  that  a  less 
quantity  passed  off  in  the  same  time,  in  the  same  way, 
through  the  bottom  of  the  instrument  No.  6,  it  ap- 
pears that  this  last-mentioned  instrument  must  have 
lost  by  radiation,  or  in  rays  which  passed  through  the  air, 
a  quantity  of  heat  =  9597. 

For  it  is  38  J  minutes    to    9919  as  37  J  minutes  to 

9597- 


94        Inquiry  concerning  the  Nature  of  Heat, 

And  if  of  the  total  quantity  of  heat  which  passed  off 
through  the  bottom  of  the  conical  instrument  No.  6,  = 
9954,  a  quantity  =  9597  passed  off  through  the  air  in 
calorific  rays,  the  remainder  only  (9954  —  959?) ,  which 
amounts  to  no  more  than  357  parts,  could  have  been 
communicated  to  the  air. 

Hence  it  would  appear  that  when  a  hot  body  is 
cooled  in  air  ^V  Part  on^y  °f  tne  neat  which  it  loses  is 
acquired  by  the  air;  for  357  is  to  9597  as  i  to  27,  very 
nearly.  But  I  shall  refrain  from  enlarging  farther  on 
this  subject  at  present. 

One  of  the  objects  which  I  had  in  view  in  the  last  ex- 
periment was  to  find  out  whether  the  cooling  of  a  hot 
body  in  air  is  or  is  not  sensibly  accelerated  or  retarded 
by  the  greater  or  lesser  distance  at  which  the  body  is 
placed  from  other  neighbouring  solid  bodies,  when  these 
neighbouring  bodies  are  at  the  same  temperature  as  the 
air;  and,  as  a  comparison  of  the  result  of  this  experi- 
ment with  the  results  of  the  two  preceding  experiments 
so  strongly  indicated  that  the  cooling  of  the  conical  ves- 
sel in  the  preceding  experiments  had  in  fact  been  re- 
tarded by  the  vicinity  of  the  pewter  platter  over  which  it 
was  suspended,  I  was  now  induced  to  repeat  these  ex- 
periments with  some  variations. 

These  investigations  appeared  to  me  to  be  of  the 
more  importance,  as  I  conceived  that  the  results  of  them 
might  lead  to  a  discovery  of  one  of  the  causes  of  the 
warmth  of  clothing. 

Experiment  No.  32.  —  I  now  placed  the  pewter  platters 
once  more  in  their  former  stations,  perpendicularly  under 
the  bottoms  of  the  two  conical  vessels,  but  at  the  dis- 
tance of  3  inches  only  ;  that  which  was  under  the  vessel 
No.  5  being  at  the  temperature  of  the  air  of  the  room 


and  the  Mode  of  its  Communication.  95 

(62°),  while  that  placed  under  the  vessel  No.  6  was  kept 
ice-cold,  by  means  of  pounded  ice  and  water,  which  was 
put  into  the  earthen  dish  on  the  brim  of  which  it  was 
supported. 

The  times  of  the  cooling  of  the  vessels,  through  the 
standard  interval  of  10  degrees,  were  as  follows  :  — 

No,  5          ......  in  40^  minutes. 

No.  6,  which  was  over  ice,  .       in  33^       " 

Experiment  No.  33.  —  I  repeated  this  experiment  once 
more,  but  varied  it  by  bringing  the  pewter  platters  still 
nearer  to  the  bottoms  of  the  conical  vessels.  The  flat 
horizontal  part  of  each  of  the  platters  was  now  only  2 
inches  below  the  flat  surface  of  the  bottom  of  the  con- 
ical vessel  which  was  suspended  over  it.  Both  the  plat- 
ters still  remained  covered  by  their  flat  circular  perforated 
covers  of  paper ;  but  it  should  be  remembered  that  the 
circular  hole  in  the  centre  of  each  of  these  covers  was  no 
less  than  6  inches  in  diameter,  and  consequently  that  a 
large  portion  of  the  flat  part  of  the  bottom  of  the  platter 
was  in  full  view  (if  I  may  use  that  expression)  of  the 
bottom  of  the  vessel  which  was  suspended  over  it. 

The  times  of  cooling  in  this  experiment  were  as  fol- 
lows :  — 

No.  5  cooled  through  the  given  interval  in  42^  minutes. 
No.  6,  which  was  over  ice,       .         .       in   32^       " 

The  results  of  these  experiments  show  (what  indeed 
might  have  been  expected,  especially  on  the  supposition 
that  the  heating  and  cooling  of  bodies  is  effected  by 
means  of  radiations)  that,  although  the  cooling  of  the  hot 
body  suspended  over  a  surface  kept  constantly  cold  by 
artificial  means  was  accelerated  by  being  brought  nearer 
to  that  cold  surface,  yet,  in  a  case  where  the  cold  surface 


96        Inquiry  concerning  the  Nature  of  Heat, 

was  less  intensely  cold,  and  where  its  temperature  could 
be  sensibly  raised  by  the  calorific  rays  from  the  hot  body, 
the  cooling  of  the  hot  body  was  retarded  by  a  nearer 
approach  of  that  cold  surface. 

From  the  results  of  these  experiments  we  may  safely 
conclude  that,  if  the  hot  body,  instead  of  being  a  conical 
vessel  covered  up  on  all  sides  except  its  flat  bottom, 
had  been  a  globe,  and  if  this  hot  globe  had  been  sus- 
pended in  the  centre  of  another  larger  thin  hollow  sphere 
(this  last  being,  at  the  beginning  of  the  experiment,  at 
the  same  temperature  as  the  air  and  walls  of  the  room), 
the  vicinity  of  the  surface  of  this  hollow  globe  to  the 
surface  of  the  hot  body  would  have  retarded  the  cooling 
of  the  hot  body  in  the  same  manner  as  the  cooling  of 
the  conical  vessel  No.  5  was  retarded  in  the  foregoing 
experiments ;  and  if,  instead  of  inclosing  the  hot  body 
in  the  centre  of  a  single  hollow  sphere  of  any  given 
thickness,  it  were  placed  in  the  common  centre  of  a 
number  of  much  thinner  concentric  spheres,  of  different 
diameters,  the  time  of  cooling  would  be  still  more  re- 
tarded. 

By  tracing  the  various  operations  which  would  take 
place  in  the  cooling  of  the  hot  body  in  this  imaginary 
experiment,  we  shall  become  acquainted  with  the  nature 
of  those  which  actually  take  place  when  the  cooling  of  a 
hot  body  is  prolonged  by  means  of  warm  clothing. 

From  the  results  of  several  of  the  foregoing  experi- 
ments we  may  conclude  that,  supposing  the  thin  con- 
centric hollow  spheres  in  which  the  hot  body  is  confined 
to  be  made  of  metal,  the  cooling  will  be  slower  if  the  sur- 
faces of  these  spheres  are  polished  than  if  they  are  unpol- 
ished or  blackened  ;  and  hence  we  might  very  naturally 
be  led  to  suspect  (what  is  probably  true  in  fact)  that  the 


and  the  Mode  of  its  Communication.  97 

warmth  of  any  kind  of  substance  used  as  clothing,  or  its 
power  of  preventing  our  bodies  from  being  cooled  by 
the  influence  (frigorific  radiations)  of  surrounding  colder 
bodies,  depends  very  much  on  the  polish  of  its  surface. 

If,  with  the  assistance  of  a  microscope,  we  examine 
those  substances  which  supply  us  with  the  warmest  cov- 
erings, —  such,  for  instance,  as  furs,  feathers,  silk,  &c., — 
we  shall  find  their  surfaces  not  only  smooth,  but  also  very 
highly  polished  ;  we  shall  also  find  that,  other  circum- 
stances being  equal,  those  substances  are  the  warmest 
which  are  the  finest,  or  which  are  composed  of  the  great- 
est number  of  fine  polished  detached  threads  or  fibres. 

The  fine  white  shining  fur  of  a  Russian  hare  is  much 
warmer  than  coarse  hair;  and  fine  silk,  as  spun  by  the 
silkworm  is  warmer  than  the  same  silk  twisted  together 
into  coarse  threads ;  as  I  found  by  actual  experiments, 
an  account  of  which  has  already  been  laid  before  this 
Society  and  published  in  the  Philosophical  Transactions. 

I  formerly  considered  the  warmth  of  natural  and  ar- 
tificial clothing  as  depending  •principally  on  the  obstacle 
it  opposes  to  the  motions  of  the  cold  air  by  which  the 
hot  body  is  surrounded ;  but,  by  a  patient  and  careful 
examination  of  the  subject,  I  have  been  convinced  that 
the  efficacy  of  radiation  is  much  greater  than  I  had  sup- 
posed it  to  be. 

From  the  result  of  the  experiment  No.  31,  we  might 
be  led  to  conclude  that  a  very  small  part  only  of  the 
heat  which  a  hot  body  appears  to  lose  when  it  is  cooled 
in  air  is  in  fact  communicated  to  that  fluid,  a  much 
greater  portion  of  it  being  communicated  to  other  sur- 
rounding bodies  at  a  distance ;  and,  in  one  of  my  for- 
mer experiments,  a  hot  body  was  cooled,  though  it  was 
placed  in  a  Torricellian  vacuum. 

VOL     II.  7 


98        Inquiry  concerning  the  Nature  of  Heat, 

These  researches  appear  to  me  to  be  the  more  inter- 
esting, as  I  have  long  been  of  opinion  that  it  must  be 
by  experiments  of  this  kind  (showing  in  what  manner 
the  temperature  of  bodies  are  affected  reciprocally  at 
different  degrees  of  temperature  and  at  different  dis- 
tances) that  the  hypothesis  of  radiation  must  be  estab- 
lished or  proved  to  be  unfounded. 

When  I  speak  of  heat  as  being  communicated  to  air 
immediately  by  a  'hot  body  which  is  cooled  in  it,  I  mean 
only  that  it  is  not  first  communicated  to  other  neighbour- 
ing bodies,  and  then  given  by  them  to  the  particles  of  air 
with  which  they  happen  to  be  in  contact.  In  this  last- 
mentioned  way  much  of  the  heat,  no  doubt,  which  a  hot 
body  loses  when  cooled  in  air  is  ultimately  communi- 
cated to  that  fluid. 

I  am  far  from  supposing  that  the  particles  of  air 
which,  coming  into  contact  with  a  hot  body,  are  heated 
in  consequence  of  that  near  approximation  receive  heat 
in  any  other  manner  than  that  in  which  other  bodies  at  a 
greater  distance  receive  it.  If  in  the  one  case  it  be  gen- 
erated or  excited  by  the  agency  of  calorific  rays  or  un- 
dulations caused  by  the  hot  body,  it  must,  I  am  per- 
suaded, be  excited  in  the  same  manner  in  the  other. 

The  reason  why  the  particle  of  air  which  is  in  imme- 
diate contact  with  a  hot  body  is  heated,  while  other  par- 
ticles near  it  are  not  affected  by  the  calorific  rays  from 
the  hot  body  which  are  continually  passing  by  them 
through  the  air,  is,  I  conceive,  because  the  particle 
heated  is  at  the  surface  of  the  fluid  (air),  where  these  rays 
are  either  reflected,  refracted,  or  absorbed ;  but  when  a 
ray  has  once  passed  the  surface  of  a  transparent  fluid,  it 
proceeds  straight  forward,  without  being  farther  affected 
by  it,  and  consequently  without  affecting  it,  till  it  conies  to 


and  the  Mode  of  its  Communication.  99 

the  confines  of  the  medium,  or  to  the  surface  of  some 
other  body. 

If  this  hypothesis  of  the  communication,  or  rather 
generation,  of  heat  and  of  cold  by  radiation  be  true, 
it  will  enable  us  to  explain,  in  a  satisfactory  manner, 
what  has  been  called  the  non-conducting  power  of  trans- 
parent fluids  with  respect  to  heat ;  for,  if  heat  be  real- 
ly communicated  or  excited  in  the  manner  above  de- 
scribed, it  is  quite  evident  that  a  perfectly  transparent 
fluid  can  receive  heat  only  at  its  surface,  and,  conse- 
quently, that  heat  cannot  be  propagated  in  such  a  fluid 
by  communication  from  one  particle  of  the  fluid  to  an- 
other. 

By  a  transparent  fluid  I  mean  such  an  one  as  admits 
the  calorific  and  frigorific  rays  emitted  by  hot  and  by 
cold  bodies  to  pass  freely  through  it  without  obstruct- 
ing their  passage  or  diminishing  their  intensities. 

Whether  any  of  the  fluids  with  which  we  are  ac- 
quainted be  perfectly  transparent  in  this  sense  of  the 
word  or  not,  I  will  not  pretend  to  say ;  but  there  is 
reason  to  think  that  pure  water  and  air  and  most  other 
fluids  which  are  transparent  to  light,  possess  a  high  de- 
gree of  transparency  in  regard  to  calorific  and  frigorific 
rays,  or  that  they  give  a  very  free  passage  to  them  when 
they  have  once  passed  their  surfaces. 

An  even  or  polished  surface  has  been  found  to  facili- 
tate very  much  the  reflection  of  the  rays  of  light.  May 
it  not,  in  all  cases,  have  an  equal  tendency  to  facilitate 
the  reflection  of  calorific  and  frigorific  rays  ? 

In  the  experiments  with  the  large  cylindrical  vessels, 
where  they  were  exposed  naked  to  cool  in  the  air,  their 
surfaces  were  polished,  and  they  were  a  long  time  in 
cooling.  But,  when  the  surface  of  the  vessel  was  black- 


TOO       Inquiry  concerning  Ike  Nature  of  Heat, 

ened  or  covered  with  other  substances,  the  vessel  was 
found  to  cool  much  more  rapidly. 

A  large  proportion  of  the  frigorific  rays  from  the  sur- 
rounding colder  bodies  were,  in  the  former  case,  reflected 
at  the  polished  surface  of  the  metallic  vessel ;  but,  in 
the  latter  case,  more  of  them  were  absorbed. 

When  a  large  drop  of  water  rolls  about  without  being 
evaporated  upon  the  flat  surface  of  a  piece  of  red-hot 
iron,  the  surface  of  the  drop  is  polished;  and,  the  calo- 
rific rays  being  mostly  reflected,  the  water  is  very  little 
heated,  notwithstanding  the  extreme  intensity  of  the  heat 
of  the  iron  and  its  nearness  to  the  water. 

If  the  iron  be  less  hot,  the  water  penetrates  the  pores 
of  the  oxide  which  covers  the  metal,  the  drop  ceases  to 
have  a  polished  surface,  acquires  heat  very  rapidly,  and 
is  soon  evaporated. 

If  a  drop  of  water  be  placed  on  the  clean  and  polished 
surface  of  a  metal  not  so  easily  oxidable  as  iron,  it  will 
retain  its  spherical  form  and  polished  surface  under  a 
lower  degree  of  temperature  than  on  iron  ;  and  conse- 
quently will  be  less  heated,  and  less  rapidly  evaporated 
by  a  moderate  heat. 

If  a  large  drop  of  water  be  put  carefully  into  a  clean 
silver  spoon,  previously  heated  very  hot  (that  is  to  say, 
so  hot  as  to  give  a  loud  hissing  noise  when  touched  with 
the  wetted  finger,  but  much  below  the  heat  of  red-hot 
metal),  the  drop  will  support,  or  rather  resist,  this  heat 
for  a  considerable  time ;  but  after  the  spoon  has  been 
suffered  to  cool  down  nearly  to  the  temperature  of  boil- 
ing water  a  drop  of  water  put  into  it  will  be  evaporated 
instantaneously. 

It  appears,  from  the  results  of  these  experiments,  to 
be  probable  that  under  high  temperatures  air  is  attracted 


and  the  Mode  of  its  Communication.         101 

by  metals  so  much  more  strongly  than  water  that  even 
the  weight  of  a  drop  of  water  is  not  sufficient  to  force 
away  the  stratum  of  air  which  covers  and  adheres  to  the 
surface  of  a  metal  on  which  the  drop  reposes;  but  at 
lower  temperatures  this  does  not  seem  to  be  the  case. 

The  following  experiment,  which  I  made  several 
months  ago  with  a  view  to  investigate  the  cause  of  the 
slow  evaporation  of  drops  of  water  placed  on  hot  metals, 
will,  I  think,  throw  much  light  on  this  subject. 

Experiment  No.  34.  —  Taking  a  clean  polished  silver 
spoon,  I  blackened  the  inside  of  it  by  holding  it  over 
the  flame  of  a  wax  candle  ;  then,  putting  a  large  drop  of 
water  into  it,  I  found,  as  I  expected,  that  the  drop  took 
a  spherical  form,  and  rolled  about  in  the  spoon  without 
wetting  its  blackened  surface. 

I  now  held  the  spoon  over  the  flame  of  a  candle,  and 
attempted  to  make  the  water  boil ;  but  I  found  it  to  be 
absolutely  impossible.  The  handle  of  the  spoon  became 
so  very  hot  that  I  could  not  hold  it  in  my  hand  without 
being  burnt,  though  it  was  wrapped  up  in  three  or  four 
thicknesses  of  linen  ;  but  still  the  drop  of  water  did  not 
appear  to  be  at  all  affected  by  this  intense  heat.  If  the 
bowl  of  the  spoon  were  touched  with  the  finger,  a  hissing 
noise  announced  that  it  was  extremely  hot ;  but  still  the 
water  remained  perfectly  quiet  in  the  spoon  without  be- 
ing evaporated. 

Having  in  vain  attempted  to  make  this  drop  of  water 
boil,  and  not  being  able  to  hold  the  spoon  over  the 
flame  of  the  candle  any  longer  on  account  of  the  heat  of 
its  handle,  I  now  poured  the  drop  into  the  palm  of  my 
hand.  I  found  it  to  be  warm,  but  by  no  means  scald- 
ing hot. 

By  holding  the  spoon  with  a  pair  of  tongs  over  the 


IO2      Inquiry  concerning  the  Nature  of  Heat, 

flame  of  the  candle  for  a  longer  time,  I  found  that  a 
drop  of  water  in  the  spoon  gradually  changed  its  form, 
became  less,  and  was  at  length  evaporated  ;  from  be- 
ing spherical  and  lucid,  it  gradually  took  an  oblong  form, 
and  its  surface  became  obscure ;  and  when  it  was  evap- 
orated it  left  a  kind  of  skin  behind  it,  which  was  evident- 
ly composed  of  the  particles  of  black  matter  which  had 
by  degrees  attached  themselves  to  its  surface,  and  which 
probably  had  contributed  not  a  little  to  its  being  at  last 
heated  and  evaporated. 

The  change  in  the  form  of  the  drop  of  water,  and 
more  especially  the  gradual  loss  of  its  lucid  appearance, 
made  me  suspect  that  it  had  turned  round  during  the 
experiment.  If  it  really  did  so  its  motion  must  either 
have  been  extremely  rapid  or  very  slow,  for,  though  I 
examined  it  with  great  attention,  I  could  not  perceive 
that  it  had  any  rotatory  motion. 

I  will  take  the  liberty  to  mention  another  little  exper- 
iment which  I  have  often  made  to  amuse  myself  and 
others,  though  it  may  perhaps  be  thought  too  trifling  to 
deserve  the  attention  of  the  Royal  Society. 

Experiment  No.  35. —  If  a  large  drop  of  water  be 
formed  at  the  end  of  a  small  splinter  of  light  wood 
(deal,  for  instance),  and  this  drop  be  thrust  quickly  in- 
to the  centre  of  the  flame  of  a  newly  snuffed  candle, 
which  burns  bright  and  clear,  the  drop  of  water  will  re- 
main for  a  considerable  time  in  the  centre  of  the  flame 
and  surrounded  by  it  on  every  side,  without  being  made 
to  boil,  or  otherwise  apparently  affected  by  the  heat ; 
and  if  it  be  taken  out  of  the  flame  and  put  upon  the 
hand,  it  will  not  be  found  to  be  scalding  hot. 

If  it  be  held  for  some  time  in  the  flame,  it  will  be 
gradually  diminished  by  evaporation  ;  but  there  is  much 


and  the  Mode  of  its  Communication.         103 

reason  to  think  that  the  heat  which  it  acquires  is  not 
communicated  to  it  by  the  flame,  but  by  the  wood  to 
which  it  adheres,  which  is  soon  heated  by  the  flame,  and 
even  set  on  fire. 

I  cannot  refrain  from  just  observing  that  it  appears  to 
me  to  be  extremely  difficult  to  reconcile  the  results  of 
any  of  the  foregoing  experiments  with  the  hypothesis 
of  modern  chemists  respecting  the  materiality  of  heat. 

Deeply  sensible  of  the  insufficiency  of  the  powers  of 
the  human  mind  to  unfold  the  mysteries  of  nature  and 
discover  the  agents  she  employs  and  their  mode  of  ac- 
tion in  her  secret  and  invisible  operations,  and  being, 
moreover,  fully  aware  of  the  danger  of  forming  an  at- 
tachment to  a  false  theory,  and  of  the  folly  of  wasting 
time  in  idle  speculation,  I  have  ever,  in  my  philosoph- 
ical researches,  been  much  more  anxious  to  discover 
new  facts,  and  to  show  how  the  discoveries  of  others 
may  be  made  useful  to  mankind,  than  to  invent  plau- 
sible theories,  which  much  oftener  tend  to  misguide  than 
to  lead  us  in  the  path  of  truth  and  science. 

There  are,  however,  situations  in  which  an  experi- 
mental inquirer  sometimes  finds  himself,  where  it  is 
almost  impossible  for  him  to  abstain  from  forming  or 
adopting  some  general  theory  for  the  purpose  of  ex- 
plaining the  phenomena  which  fall  under  his  observa- 
tion, and  directing  him  in  his  future  researches. 

Finding  myself  in  that  situation  at  this  time,  I  beg 
the  attention  and,  above  all,  the  indulgence  of  the  Society 
while  I  endeavour  to  explain  the  conjectures  I  have 
formed  respecting  the  nature  of  heat  and  the  mode  of 
its  communication. 

Hot  and  cold,  like  fast  and  slow,  are  mere  relative 
terms ;  and,  as  there  is  no  relation  or  proportion  be- 


IO4      Inquiry  concerning  the  Nature  of  Heat, 

tween  motion  and  a  state  of  rest,  so  there  can  be  no 
relation  between  any  degree  of  heat  and  absolute  cold, 
or  a  total  privation  of  heat ;  hence  it  is  evident  that 
all  attempts  to  determine  the  place  of  absolute  cold,  on 
the  scale  of  a  thermometer,  must  be  nugatory. 

It  seems  probable  that  motion  is  an  essential  quality 
of  matter,  and  that  rest  is  nowhere  to  be  found  in  the 
universe. 

We  well  know  that  all  those  bodies  which  fall  under 
the  cognizance  of  our  senses  are  in  motion  ;  and  there 
are  many  appearances  which  seem  to  indicate  that  the 
constituent  particles  of  all  bodies  are  also  impressed 
with  continual  motions  among  themselves,  and  that  it  is 
these  motions  (which  are  capable  of  augmentation  and 
diminution)  that  constitute  the  heat  or  temperature  of 
sensible  bodies. 

The  only  effects  of  which  we  have  any  idea  result- 
ing from  the  action  of  one  body  on  another  are  a  change 
of  velocity  or  a  change  of  direction,  or  both.  We  per- 
ceive, it  is  true,  that  certain  bodies  have  a  power  of 
affecting  certain  other  bodies  at  a  distance;  but  this  is 
no  proof  that  the  effects  produced  are  essentially  differ- 
ent from  those  which  result  from  collision ;  for,  if  an 
elastic  body  be  interposed  between  the  two  bodies,  their 
actions  on  each  other  may  be  communicated  through 
such  intermediate  elastic  body,  which,  when  the  action 
is  at  an  end,  and  the  effects  resulting  from  it  on  the 
two  bodies  have  taken  place,  will  be  in  the  same  state 
precisely  in  which  it  was  before  the  action  began. 

If  a  bell  or  any  other  solid  body,  perfectly  elastic, 
placed  in  a  perfectly  elastic  fluid,  and  surrounded  by 
other  perfectly  elastic  solid  bodies,  were  struck  and 
made  to  vibrate,  its  vibrations  would  by  degrees  be 


and  the  Mode  of  its  Communication.          105 

communicated,  by  means  of  the  undulations  or  pulsa- 
tions they  would  occasion  in  the  elastic  fluid  medium, 
to  the  other  surrounding  solid  and  elastic  bodies.  If 
these  surrounding  bodies  should  happen  to  be  already 
vibrating,  and  with  the  same  velocity  as  that  with  which 
the  bell  is  made  to  vibrate  by  the  blow,  the  undulations 
in  the  elastic  fluid  occasioned  by  the  bell  would  neither 
increase  nor  diminish  the  velocity  or  frequency  of  the 
vibrations  of  the  surrounding  bodies  ;  neither  would 
the  undulations  caused  by  the  vibrations  of  these  bodies 
tend  to  accelerate  or  to  retard  the  vibrations  of  the 
bell.  But  if  the  vibrations  of  the  bell  were  more  fre- 
quent than  those  of  the  surrounding  bodies,  the  undu- 
lations it  would  occasion  in  the  elastic  fluid  would  tend 
to  accelerate  the  vibrations  of  the  surrounding  bodies ; 
on  the  other  hand,  the  undulations  occasioned  by  the 
slower  vibrations  of  the  surrounding  bodies  would  re- 
tard the  vibrations  of  the  bell,  and  the  bell  and  the 
surrounding  bodies  would  continue  to  affect  each  other 
until,  by  the  vibrations  of  the  latter  being  gradually 
increased  and  those  of  the  former  diminished,  in  con- 
sequence of  their  actions  on  each  other,  they  would  all 
be  reduced  to  the  same  tone. 

Supposing  now  that  heat  be  nothing  more  than  the 
motions  of  the  constituent  particles  of  bodies  among 
themselves  (an  hypothesis  of  ancient  date,  and  which 
always  appeared  to  me  to  be  very  probable),  if  for  the 
bell  we  substitute  a  hot  body,  the  cooling  of  it  will  be 
attended  by  a  series  of  actions  and  reactions  exactly 
similar  to  those  just  described. 

The  rapid  undulations  occasioned  in  the  surrounding 
ethereal  fluid,  by  the  swift  vibrations  of  the  hot  body, 
will  act  as  calorific  rays  on  the  neighbouring  colder  solid 


io6       Inquiry  concerning  the  Natiire  of  Heat, 

bodies,  and  the  slower  undulations,  occasioned  by  the 
vibrations  of  those  colder  bodies,  will  act  as  frigorific 
rays  on  the  hot  body  ;  and  these  reciprocal  actions  will 
continue,  but  with  decreasing  intensity,  till  the  hot 
body  and  those  colder  bodies  which  surround  it  shall, 
in  consequence  of  these  actions,  have  acquired  the  same 
temperature,  or  until  their  vibrations  have  become  iso- 
chronous. 

According  to  this  hypothesis,  cold  can  with  no  more 
propriety  be  considered  as  the  absence  of  heat  than  a 
low  or  grave  sound  can  be  considered  as  the  absence  of 
a  higher  or  more  acute  note  ;  and  the  admission  of  rays 
which  generate  cold  involves  no  absurdity  and  creates 
no  confusion  of  ideas. 

On  a  superficial  view  of  the  subject,  it  may  perhaps 
appear  difficult  to  reconcile  solidity,  hardness,  and  elas- 
ticity with  those  never-ceasing  motions  which  we  have 
supposed  to  exist  among  the  constituent  particles  of  all 
bodies ;  but  a  patient  investigation  of  the  matter  will 
show  that  the  admission  of  that  supposed  fact,  instead 
of  rendering  it  more  difficult  to  form  distinct  and  satis- 
factory ideas  of  the  causes  on  which  those  qualities  of 
bodies  depend,  will  rather  facilitate  those  abstruse  re- 
searches. 

Judging  from  all  the  operations  of  nature,  of  the  causes 
of  which  we  are  able  to  form  any  distinct  ideas,  we  are 
certainly  led  to  conclude  that  the  force  of  dead  matter 
(and  perhaps  of  living  matter  also),  or  its  power  of 
affecting,  that  is  to  say,  of  moving  other  matter,  or  of 
resisting  its  impulse,  depends  on  its  motion. 

If,  therefore,  solid  (or  fluid)  bodies  have  any  powers 
whatever,  either  of  impulse  or  of  resistance,  it  appears 
to  me  to  be  more  reasonable  to  ascribe  them  to  the 


and  the  Mode  of  its  Communication.         107 

living  forces  residing  in  them  —  to  the  never-ceasing 
motions  of  their  constituent  particles  —  than  to  sup- 
pose them  to  be  derived  from  their  want  of  power,  and 
their  total  indifference  to  motion  and  to  rest. 

No  reasonable  objection  against  this  hypothesis  (of 
the  incessant  motions  of  the  constituent  particles  of  all 
bodies),  founded  on  a  supposition  that  there  is  not 
room  sufficient  for  these  motions,  can  be  advanced ; 
for  we  have  abundant  reason  to  conclude  that  if  there 
be  in  fact  any  indivisible  solid  particles  of  matter 
(which,  however,  is  very  problematical),  these  particles 
must  be  so  extremely  small,  compared  to  the  spaces 
they  occupy,  that  there  must  be  ample  room  for  all 
kinds  of  motions  among  them. 

And  whatever  the  nature  or  directions  of  these  inter- 
nal motions  may  be  among  the  constituent  particles  of 
a  solid  body,  as  long  as  these  constituent  particles,  in 
their  motions,  do  not  break  loose  from  the  systems  to 
which  they  belong  (and  to  which  they  are  attached  by 
gravitation),  and  run  wild  in  the  vast  void  by  which 
each  system  is  bounded  (which,  as  long  as  the  known 
laws  of  nature  exist,  is  no  doubt  impossible),  the  form 
or  external  appearance  of  the  solid  cannot  be  sensibly 
changed  by  them. 

But  if  the  motions  of  the  constituent  particles  of  any 
solid  body  be  either  increased  or  diminished,  in  conse- 
quence of  the  actions  or  radiations  of  other  distant 
bodies,  this  event  could  not  happen  without  producing 
some  visible  change  in  the  solid  body. 

If  the  motions  of  its  constituent  particles  were  dimin- 
ished by  these  radiations,  it  seems  reasonable  to  con- 
clude that  their  elongations  would  become  less,  and 
consequently  that  the  volume  of  the  body  would  be 


1 08      Inqziiry  concerning  the  Nature  of  Heat., 

contracted ;  but  if  the  motions  of  these  particles  were 
increased,  we  might  conclude,  a  •priori,  that  the  volume 
of  the  body  would  be  expanded. 

We  have  not  sufficient  data  to  enable  us  to  form  dis- 
tinct ideas  of  the  nature  of  the  change  which  takes  place 
when  a  solid  body  is  melted ;  but  as  fusion  is  occa- 
sioned by  heat,  that  is  to  say,  by  an  augmentation  (from 
without)  of  that  action  which  occasions  expansion  if 
expansion  be  occasioned  by  an  increase  of  the  motions 
of  the  constituent  particles  of  the  body,  it  is,  no  doubt, 
a  certain  additional  increase  of  those  motions  which 
causes  the  form  of  the  body  to  be  changed,  and  from 
a  solid  to  become  a  fluid  substance. 

As  long  as  the  constituent  particles  of  a  solid  body 
which  are  at  the  surface  of  that  body  do  not,  in  their 
motions,  pass  by  each  other  ^  the  body  must  necessarily 
retain  its  form  or  shape,  however  rapid  those  motions 
or  vibrations  may  be ;  but  as  soon  as  the  motion  of 
these  particles  is  so  augmented  that  they  can  no  longer 
be  restrained  or  retained  within  these  limits,  the  regular 
distribution  of  the  particles  which  they  acquired  in 
crystallization  is  gradually  destroyed,  and  the  particles 
so  detached  from  the  solid  mass  form  new  and  inde- 
pendent systems,  and  become  a  liquid  substance. 

Whatever  may  be  the  figures  of  the  orbits  which  the 
particles  of  a  liquid  describe,  the  mean  distances  of 
those  particles  from  each  other  remain  nearly  the  same 
as  when  they  constituted  a  solid,  as  appears  by  the 
small  change  of  specific  gravity  which  takes  place  when 
a  solid  is  melted  and  becomes  a  liquid ;  and,  on  a  sup- 
position that  their  motions  are  regulated  by  the  same 
laws  which  regulate  the  solar  system,  it  is  evident  that 
the  additional  motion  they  must  necessarily  acquire,  in 


and  the  Mode  of  its  Communication.         109 

order  to  their  taking  the  fluid  form,  cannot  be  lost,  but 
must  continue  to  reside  in  the  liquid,  and  must  again 
make  its  appearance  when  the  liquid  changes  its  form 
and  becomes  a  solid. 

It  is  well  known  that  a  certain  quantity  of  heat  is 
requisite  to  melt  a  solid,  which  quantity  disappears  or 
remains  latent  in  the  liquid  produced  in  that  process ; 
and  that  the  same  quantity  of  heat  reappears  when  this 
liquid  is  congealed  and  becomes  a  solid  body. 

But  before  I  proceed  any  farther  in  these  abstruse 
speculations,  I  shall  endeavour  to  investigate  some  of 
the  consequences  which  would  necessarily  result  from 
the  radiations  of  hot  and  of  cold  bodies,  supposing 
those  radiations  to  exist,  and  their  motions  and  actions 
to  be  regulated  by  certain  assumed  laws. 

And  first,  it  is  evident  that  the  intensity  of  the  rays 
emitted  by  a  luminous  point,  in  a  perfectly  transparent 
medium,  is  everywhere  as  the  squares  of  the  distance 
from  that  point  inversely ;  for  the  intensity  of  those 
rays  must  be  as  their  condensation  ;  and  their  con- 
densation being  diminished  in  proportion  as  the  space 
they  occupy  is  increased,  if  we  suppose  all  the  rays 
which  proceed  in  all  directions  from  any  point  to  set 
out  at  the  same  instant  and  to  move  with  the  same 
velocity  in  right  lines,  these  simultaneous  rays  (or  un- 
dulations) will  in  their  progress  form  a  sphere,  which 
sphere  will  increase  continually  in  size  as  the  rays  ad- 
vance ;  and  as  all  the  rays  must  be  found  at  the  surface 
of  this  sphere,  their  intensity  or  condensation  must 
necessarily  be  as  the  surface  of  the  sphere  inversely,  or 
as  the  squares  of  the  distance  inversely  from  the  centre 
of  the  sphere,  or,  which  is  the  same  thing,  from  the 
luminous  point  from  which  these  rays  proceed  ;  the 


no      Inquiry  concerning  the  Nature  of  Heat, 

surfaces  of  spheres  being  to  each  other  as  the  squares 
of  their  radii. 

Supposing  now  (what,  indeed,  appears  to  be  incontro- 
vertible) that  the  intensity  of  the  rays  which  hot  and 
cold  bodies  emit,  in  a  medium  perfectly  transparent, 
follows  the  same  law,  we  can  determine  what  effects 
must  be  produced  by  the  largeness  or  smallness  of  the 
confined  space  (of  a  room,  for  instance)  in  which  a  hot 
body  is  placed  to  cool. 

To  simplify  this  investigation,  we  will  suppose  this 
confined  space  to  be  a  hollow  sphere  of  ice  9  feet  in 
diameter,  at  the  temperature  of  freezing  water ;  and  the 
hot  body  to  be  a  solid  sphere  of  metal  2  inches  in 
diameter,  at  the  temperature  of  boiling  water,  placed  in 
the  centre  of  it ;  and  we  will  suppose,  farther,  that  this 
hollow  sphere  is  void  of  air,  and  that  the  cooling  of  the 
hot  body  is  effected  solely  by  the  frigorific  rays  from 
the  ice. 

The  question  to  be  determined  is,  in  what  manner 
the  cooling  of  the  hot  body  would  be  affected  by  in- 
creasing the  diameter  of  this  hollow  sphere  of  ice. 

Let  us  suppose  its  diameter  to  be  increased  to  18 
feet.  Its  internal  surface  will  then  be  to  the  surface  of 
a  sphere  9  feet  in  diameter  as  the  square  of  18  to  the 
square  of  9,  that  is  to  say,  as  324  to  8 1,  or  as  4  to  i. 
And  as  the  quantity  of  frigorific  rays  emitted  are,  c<eteris 
•paribus,  as  the  surface  from  which  they  proceed,  the 
quantity  of  rays  emitted  by  the  internal  surface  of  the 
larger  sphere  will  be  to  the  quantity  emitted  by  the. 
internal  surface  of  the  smaller  as  4  to  I. 

But  the  intensities  of  these  rays  at  the  common  cen- 
tre of  these  spheres  (where  the  hot  body  is  placed)  be- 
ing as  the  squares  of  the  distances  from .  the  radiating 


and  the  Mode  of  its  Communication.         1 1 1 

points  inversely,  the  intensity  of  the  rays  from  the 
internal  surface  of  the  smaller  sphere  must  be  to  the 
intensity  of  the  rays  from  the  internal  surface  of  the 
larger  sphere  as  4  to  i,  at  the  common  centre  of  those 
spheres. 

Now,  as  the  time  of  the  cooling  of  the  hot  body  will 
depend  on  the  quantity  of  frigorific  rays  which  arrive  at 
its  surface,  and  on  the  intensity  of  their  action,  and  as 
the  intensity  of  the  rays  from  the  internal  surface  of  the 
sphere  at  its  centre  is  diminished  in  the  same  propor- 
tion as  the  surface  of  the  sphere  is  augmented  when  its 
diameter  is  increased,  it  follows  that  a  hot  body  placed 
in  the  centre  of  a  hollow  sphere  at  any  given  constant 
temperature  below  that  of  the  hot  body,  will  be  cooled 
in  the  same  time,  or  with  the  same  celerity,  whatever 
may  be  the  size  of  the  sphere. 

If  this  conclusion  be  well  founded  (and  I  see  no  rea- 
son to  suspect  that  it  is  not  so),  it  will  follow,  from  the 
principles  assumed,  that  the  hot  body  will  be  cooled  in 
the  same  time,  in  whatever  part  of  the  hollow  sphere  it 
be  situated.  And  as  the  cooling  of  the  body  is  not 
affected,  that  is  to  say,  accelerated  or  retarded,  either  by 
the  greater  or  smaller  size  of  the  enclosed  space  in 
which  it  is  confined,  or  by  its  situation  in  that  confined 
space,  so  it  cannot  be  in  any  manner  affected  either 
by  the  form  of  that  hollow  space  or  by  the  presence  of 
a  greater  or  less  number  of  other  solid  bodies;  provided 
always,  that  all  these  surrounding  bodies  be  at  the  same 
constant  temperature. 

If,  however,  any  of  these  surrounding  bodies,  the 
temperature  of  which  is  liable  to  be  sensibly  changed 
during  the  experiment  by  the  calorific  rays  emitted  by 
the  hot  body,,  be  placed  very  near  that  body,  the  cooling 


1 1 2       Inquiry  concerning  the  Nature  of  Heat, 

of  that  hot  body  will  be  retarded,  the  rays  from  this 
neighbouring  body,  so  heated,  being  less  frigorific  than 
those  from  other  bodies  at  a  greater  distance,  which  it 
intercepts. 

The  results  of  all  my  experiments  on  the  cooling 
of  bodies  tended  uniformly  to  confirm  the  above  con- 
clusions. 

Admitting  that  the  cooling  of  a  hot  body  is  effected 
solely  by  the  rays  which  proceed  from  colder  bodies, 
and  that  these  rays,  like  those  of  light,  are  reflected, 
refracted,  and  concentrated,  according  to  certain  known 
laws,  by  the  polished  surfaces  of  mirrors  and  lenses,  it 
might  perhaps  be  imagined  that  the  cooling  of  a  hot 
body  might  be  accelerated  or  retarded  by  giving  it 
some  peculiar  form  ;  or  by  placing  near  it,  and  in  cer- 
tain positions  with  respect  to  it,  two  or  more  highly 
polished  reflecting  mirrors. 

As  these  conjectures,  if  well  founded,  might  lead  to 
experiments  from  the  results  of  which  the  truth  or  false- 
hood of  the  hypothesis  in  question  might  be  demon- 
strated, it  is  of  much  importance  that  this  matter  should 
be  thoroughly  investigated.  I  shall  therefore  beg  the 
indulgence  of  the  Society  while  I  endeavour  to  examine 
it  with  that  careful  attention  which  it  appears  to  me  to 
deserve. 

When  different  solid  substances,  heated  to  the  same 
degree  of  temperature,  are  exposed  in  the  air  to  cool, 
those  among  them  which  appear  to  the  touch  to  be  the 
hottest  are  not  those  which  cool  the  fastest,  or  which 
send  off  calorific  rays  through  the  air  in  the  greatest 
abundance. 

As  polished  metals  reflect  a  great  part  of  the  rays 
from  other  bodies  which  arrive  at  their  surfaces,  and  as 


and  the  Mode  of  its  Communication.         1 1 3 

they  are  neither  heated  nor  cooled  by  the  rays  so  re- 
flected, their  temperatures  are  slowly  changed  by  the 
actions  of  the  surrounding  bodies  at  a  different  tem- 
perature. 

When  a  hot  polished  metallic  body  is  exposed  in  the 
air  to  cool,  surrounded  by  other  bodies  at  the  same 
temperature  as  that  of  the  cold  air,  most  of  the  rays 
from  the  surrounding  bodies  are  reflected  at  the  pol- 
ished surface  of  the  hot  body ;  it  is  evident,  then,  that 
two  sorts  of  rays  must  proceed  from  the  surface  of  that 
body,  namely,  those  calorific  rays  which  it  emits,  and 
those  other  rays  (which  with  regard  to  the  surround- 
ing bodies  are  neither  calorific  nor  frigorific)  which  it 
reflects. 

On  a  cursory  view  of  the  subject,  one  might  be  led 
to  imagine  that,  as  the  rays  which  proceed  from  the  hot 
metallic  body  are  of  two  kinds,  the  energy  of  the  calo- 
rific rays,  which  properly  belong  to  the  hot  body,  might 
be  diminished  by  those  other  reflected  rays  by  which 
they  are  accompanied,  and  with  which  they  may  be  said 
to  be  mixed  ;  but  a  more  careful  examination  of  the 
matter  will  show  that  this  cannot  be  the  case,  that  is 
to  say,  as  long  as  all  the  surrounding  bodies  continue 
to  be  at  the  same  temperature.  If  the  temperature  of 
the  surrounding  bodies  be  different,  such  of  them  will 
be  affected  by  the  reflected  rays  as  happen  to  be  of  a 
temperature  different  from  that  from  which  the  ray 
originated ;  but  still  the  effects  produced  by  the  rays 
emitted  by  the  hot  body  will  be  the  same,  or  their 
power  of  effecting  changes  in  the  temperatures  of  other 
(hotter  or  colder)  bodies  will  remain  undiminished  and 
unchanged. 

The  reason  why  their  effects  are  not  more  powerful 

VOL.   II.  8 


H4      Inquiry  concerning  the  Nature  of  Heat, 

than  they  are  found  to  be,  is  not  because  they  are  mixed 
with  other  reflected  rays,  but  because  they  are  few,  the 
greater  part  of  the  rays  which  the  hot  body  actually 
emits  being  reflected  and  turned  back  upon  itself  by  the 
reflecting  surface  by  which  it  is  immediately  surrounded. 

The  reflecting  surface  at  which  the  rays  of  light  which 
impinge  against  the  polished  surface  of  any  solid  or 
fluid  body  are  turned  back  and  reflected  is  actually  situ- 
ated without  the  body,  and  even  at  some  distance  from 
it ;  this  has  been  proved  by  the  most  decisive  experi- 
ments ;  and  there  are  so  many  striking  analogies  be- 
tween the  rays  of  light  and  those  invisible  rays  which 
all  bodies  at  all  temperatures  appe.ar  to  emit,  that  we 
can  hardly  doubt  of  their  motions  being  regulated  by 
the  same  laws. 

Perhaps  there  may  be  no  other  difference  between 
them  than  exists  between  those  vibrations  in  the  air 
which  are  audible  and  those  which  make  no  sensible  im- 
pression on  our  organs  of  hearing. 

If  the  ear  were  so  constructed  that  we  could  hear  all 
the  motions  which  take  place  in  the  air,  we  should,  no 
doubt,  be  stunned  by  the  noise ;  and  if  our  eyes  were 
so  constructed  as  to  see  all  the  rays  which  are  emitted 
continually,  by  day  and  by  night,  by  the  bodies  which 
surround  us,  we  should  be  dazzled  and  confounded  by 
that  insupportable  flood  of  light  poured  in  upon  us  on 
every  side. 

Taking  it  for  granted  that  these  invisible  radiations 
exist,  we  will  endeavour  to  trace  the  effects  which  must 
necessarily  be  produced  by  them,  and  see  if  these  in- 
vestigations will  not  lead  us  to  a  discovery  of  the  causes 
of  some  appearances  which  have  hitherto  been  envel- 
oped in  much  obscurity. 


and  the  Mode  of  its  Communication.         1 1 5 

Suppose  two  concave  reflecting  mirrors,  of  highly 
polished  metal,  each  18  inches  in  diameter,  and  18 
inches  focal  distance,  to  be  placed  opposite  to  each 
other  at  the  distance  of  10  feet,  in  a  large  quiet  room, 
in  which  the  air  and  the  walls  of  the  room  remain  con- 
stantly at  the  same  temperature  (that  of  freezing  water, 
for  instance),  without  any  variation. 

If  we  suppose  the  floor,  ceiling,  walls  of  the  room, 
and  doors  and  windows,  to  be  lined  with  a  covering  of 
ice,  at  the  temperature  of  freezing  water,  we  can  then, 
without  any  difficulty,  conceive  that  the  temperature  of 
the  room  may  remain  the  same,  notwithstanding  the 
presence  of  hotter  bodies,  which  are  brought  into  it  for 
the  purpose  of  making  experiments. 

Let  us  now  suppose  one  of  the  mirrors  to  be  at  the 
temperature  of  freezing,  and  the  other  at  that  of  boiling 
water ;  and  let  us  see  what  effects  they  would  produce 
on  each  other  by  their  radiations. 

And  first,  with  respect  to  the  hot  mirror,  it  is  evi- 
dent that  it  will  be  cooled,  not  only  by  the  frigorific 
rays  which  proceed  from  the  cold  metal  of  which  the 
opposite  mirror  is  constructed,  but  also  by  such  of  the 
frigorific  rays  from  the  sides  of  the  room  as,  impinging 
against  the  polished  reflecting  surface  of  the  cold  mir- 
ror, and  being  reflected  by  that  surface,  happen  to  fall 
on  the  surface  of  the  hot  mirror  without  being  reflected 
by  it. 

But,  as  the  quantity  of  rays  which  the  cold  mirror 
reflects  is  greater  in  proportion  as  the  reflecting  surface 
is  more  perfect,  while  the  quantity  of  rays  emitted  by 
this  cold  mirror  is  less  in  proportion  as  its  reflecting 
surface  is  more  perfect,  it  is  extremely  probable  that  the 
total  quantity  of  frigorific  rays  (emitted  and  reflected) 


1 1 6      Inquiry  concerning  the  Nature  of  Heat, 

which,  coming  from  the  surface  of  the  cold  mirror,  im- 
pinge against  the  surface  of  the  hot  mirror,  will  be  the 
same,  whatever  may  be  the  degree  of  polish,  or  reflect- 
ing power,  of  the  cold  mirror.  And,  if  this  be  the  case, 
we  may  conclude  that  the  presence  of  this  mirror  will 
have  no  effect  whatever  on  the  hot  mirror ;  or  that  it 
will  no  more  expedite  its  cooling  than  any  other  body, 
of  any  other  form,  would  do,  at  the  same  distance  and 
occupying  the  same  space. 

It  might  perhaps  be  imagined  that  the  form  of  the 
cold  mirror  might  concentrate  the  rays  it  emits  and 
reflects,  and,  by  such  concentration,  produce  a  greater 
effect  on  the  opposite  mirror  than  if  its  surface  were 
flat,  or  of  any  other  form  ;  but  a  more  attentive  exami- 
nation of  the  matter  will  show  that  no  such  concentra- 
tion actually  takes  place :  for,  with  regard  to  those  rays 
which  are  emitted  by  this  cold  body,  as  they  proceed 
from  each  point  of  its  surface  in  all  directions^  it  is  per- 
fectly evident  that  these  are  not  concentrated ;  and  with 
respect  to  those  which  are  reflected,  it  is  equally  certain 
that  they  are  not  concentrated,  because,  in  order  to 
their  being  concentrated,  they  must  arrive  at  the  surface 
of  the  mirror  in  parallel  lines,  and  in  the  direction  of 
the  axis  of  the  mirror,  which,  under  the  given  circum- 
stances, is  evidently  impossible. 

Hence  we  see  that  the  presence  of  the  cold  mirror 
will  not  tend,  in  the  smallest  degree,  either  to  accelerate 
or  to  retard  the  cooling  of  the  hot  mirror;  that  is  to 
say,  provided  its  temperature  be  not  raised  by  the  calo- 
rific rays  from  the  hot  mirror. 

If  its  temperature  be  raised  by  those  rays,  it  will 
tend  to  retard  the  cooling  of  the  hot  mirror ;  but,  even 
in  this  case,  it  will  not  retard  it  more  than  any  other 


and  the  Mode  of  its  Communication.         1 1 7 

polished  metallic  body  would  do,  of  any  other  form, 
having  the  same  area  or  quantity  of  surface  opposed  to 
the  hot  mirror,  and  being  placed  at  the  same  distance 
from  it. 

By  a  similar  train  of  reasoning  it  may  be  shown  that 
the  form  of  the  hot  body  (that  of  a  concave  mirror)  will 
contribute  nothing  to  the  effect  it  will  produce  on  the 
cold  mirror,  in  heating  it  by  the  calorific  rays  it  emits ; 
and  that  it  will  itself  be  cooled  neither  faster  nor  slower 
on  account  of  its  peculiar  form. 

Let  us  now  suppose  both  mirrors  to  be  at  the  tem- 
perature, precisely,  of  the  room  (that  of  freezing  water), 
and  that  a  bullet,  or  other  small  body  of  a  spherical 
form,  at  the  temperature  of  boiling  water,  be  placed  in 
the  focus  of  one  of  the  mirrors,  which  mirror  we  shall 
call  A. 

As  the  rays  emitted  by  this  hot  body  are  sent  off  in 
right  lines,  in  all  directions,  in  the  same  manner  as 
light  is  emitted  by  luminous  bodies,  all  those  rays  which 
fall  on  the  concave  polished  surface  of  the  mirror  A 
will  be  reflected  (as  is  well  known)  in  lines  nearly  paral- 
lel to  the  axis  of  the  mirror  ;  they  will  consequently 
fall  on  the  concave  polished  surface  of  the  opposite 
mirror  B,  and,  being  there  again  reflected,  they  will  be 
concentrated  at  the  focus  of  the  second  mirror. 

If  now  a  sensible  thermometer,  at  the  temperature  of 
the  room,  be  placed  in  this  focus,  it  will  immediately 
begin  to  rise,  in  consequence  of  the  heat  generated  in  it 
by  the  action  of  these  calorific  rays,  so  accumulated  in 
that  place. 

If,  instead  of  being  placed  in  the  focus  of  this  second 
mirror,  the  thermometer  be  placed  at  a  very  small  dis- 
tance from  that  focus,  on  one  side  of  it,  the  instrument, 


1 1 8      Inquiry  concerning  the  Nature  of  Heat, 

however  sensible  it  may  be,  will  not  be  apparently- 
affected  by  the  rays  from  the  hot  body. 

This  experiment,  which  is  of  ancient  date,  has  often 
been  made,  and  always  with  the  same  results. 

Let  us  now  suppose  the  hot  body  to  be  removed 
from  the  focus  of  the  mirror  A,  and  that  a  colder  body 
be  substituted  in  place  of  it.  And,  in  the  first  place, 
we  will  suppose  the  temperature  of  this-  colder  body  to 
be  that  of  freezing  water,  or  just  equal  to  that  which 
reigns  in  the  room. 

As  the  rays  which  bodies  at  the  same  temperature 
send  off  from  one  to  the  other  have  no  tendency  to 
increase  or  to  diminish  the  temperature  of  those  bodies, 
the  concentration  of  rays  in  the  focus  of  the  mirror  B, 
proceeding  from  the  ice-cold  body  placed  in  the  focus 
of  the  mirror  A,  can  have  no  effect  on  a  thermometer, 
at  the  same  temperature,  which  is  exposed  to  their 
action. 

If  heat  be  a  vibratory  motion  of  the  constituent  par- 
ticles of  bodies,  and  if  the  rays  which  sensible  bodies 
send  off  in 'all  directions  be  undulations  in  an  ethereal 
elastic  fluid  by  which  they  are  surrounded,  occasioned 
by  those  motions ;  as  the  pulsations  in  this  fluid  must 
be  isochronous  with  the  vibrations  by  which  they  are 
occasioned,  these  pulsations  or  undulations  can  neither 
accelerate  nor  retard  the  vibrations  of  other  bodies  at 
the  surfaces  of  which  they  arrive,  provided  the  vibra- 
tions of  the  constituent  particles  of  such  bodies  are,  at 
that  time,  isochronous  with  the  vibrations  of  the  con- 
stituent particles  of  the  body  from  which  these  undula- 
tions proceed.  But  to  return  to  our  experiment. 

Suppose  now  that,  instead  of  this  ice-cold  body, 
another  much  colder  —  at  the  temperature  of  freezing 


cr.d  the  Mode  of  its  Communication.         1 1 9 

mercury,  for  instance  —  be  placed  in  the  focus  of  the 
mirror  A,  and  that  a  thermometer  at  the  temperature 
of  freezing  water  be  placed  in  the  focus  of  the  mirror  B  ; 
what  might  be  expected  to  be  the  result  of  this  experi- 
ment ?  —  That  the  thermometer  would  fall,  in  conse- 
quence of  its  being  cooled  by  the  accumulation  of  frigo- 
rific  rays  proceeding  from  this  very  cold  body. 

Now  this  is  what  actually  happened  in  the  celebrated 
experiment  of  my  ingenious  friend,  Professor  Pictet,  of 
Geneva. 

Several  attempts  have  been  made  to  explain  the  result 
of  that  experiment,  on  the  supposition  that  caloric  has 
a  real  or  material  existence,  and  that  radiant  heat  is  that 
substance,  emitted  and  sent  off  in  right  lines  in  all  direc- 
tions from  the  surfaces  of  hot  bodies.  But  none  of 
these  explanations  appear  to  me  to  be  satisfactory.  One 
of  the  most  plausible  of  them  is  that  which  is  founded 
on  a  supposition  that  caloric  is  emitted  continually, 
under  the  form  of  radiant  heat,  by  all  bodies,  at  all 
temperatures,  but  in  greater  abundance  by  hot  bodies 
than  by  such  as  are  colder;  and  that  a  body,  at  the 
same  time  that  it  sends  off  radiant  caloric  in  all  direc- 
tions to  the  bodies  by  which  it  is  surrounded,  receives 
it  in  return,  in  greater  or  less  quantities,  from  all  those 
bodies ;  that  in  all  cases  where  a  body,  in  any  given 
time,  receives  more  radiant  caloric  than  it  gives  off,  an 
accumulation  of  caloric  in  the  body  takes  place,  in 
consequence  of  which  accumulation  it  becomes  hotter, 
but  when  it  gives  off  more  caloric  in  any  given  time 
than  it  receives,  its  quantity  of  caloric  is  gradually  di- 
minished and  it  becomes  colder;  and  that  a  constant 
temperature  results  from  the  quantities  of  caloric  emit- 
ted and  received  continually  being  equal.  But  besides 


1 2O      Inquiry  concerning  the  Nature  of  Heat, 

the  difficulty  of  explaining  how,  or  by  what  mechanism, 
it  can  be  possible  for  the  same  body  to  receive  and 
retain,  and  reject  and  drive  away,  the  same  kind  of  sub- 
stance, at  one  and  the  same  time  (an  operation  not 
only  incomprehensible,  but  apparently  impossible,  and 
to  which  there  is  nothing  to  be  found  analogous,  to 
render  it  probable),  many  other  reasons  might  be  brought 
to  show  that  this  hypothesis  of  the  supposed  continual 
interchanges  of  caloric  between  neighbouring  bodies  is 
very  improbable;  and,  among  the  rest,  there  is  one  which 
appears  to  me  to  be  quite  conclusive. 

As  the  point  in  dispute  seems  to  be  of  great  impor- 
tance to  the  science  of  heat,  I  shall  endeavour  to  ex- 
amine it  with  all  possible  attention;  and,  in  order  to 
put  the  hypothesis  in  question  to  the  test,  we  will  see 
if  it  will  accord  with  the  results  of  some  of  the  fore- 
going experiments,^  which,  in  order  to  their  being  more 
easily  comprehended  and  examined,  I  shall  elucidate  by 
figures. 

Let  the  two  opposite  ends  of  the  cylinders  A  and  B 
(Plate  III.  Fig.  4)  represent  the  two  vertical  metallic 
disks  of  equal  dimensions,  which  were  presented  at  the 
same  time  to  the  ball  of  the  thermoscope  C,  in  the  ex- 
periment No.  23. 

In  that  experiment  the  disk  A  being  at  the  tempera- 
ture of  32°  F.  (that  of  freezing  water),  and  the  disk  B 
at  112°  F.,  while  the  ball  of  the  thermoscope  C  and  all 
other  surrounding  bodies  were  at  72°,  it  was  found  that 
the  temperature  of  the  thermoscope  was  not  changed  by 
the  simultaneous  actions  of  these  two  bodies,  the  one 
hot  and  the  other  cold. 

In  order  to  account  for  this  result  on  the  hypothesis 
before  mentioned,  we  must  begin  by  supposing  that  the 


PLATE  III. 


A  FiaJ\ 


V  B 


/ly 


V/  B 


and  the  Mode  of  its  Communication.         121 

ball  of  the  thermoscope  gives  off  radiant  caloric  con- 
tinually in  all  directions,  and  receives  it  in  return  from 
the  surfaces  of  all  the  bodies  by  which  it  is  surrounded. 

With  regard  to  all  these  surrounding  bodies  (ex- 
cepting the  disks  A  and  B),  as  they  are  at  the  same 
temperature  as  the  ball  of  the  thermoscope  (that  of  7.2°), 
they  will  give  continually  to  that  instrument  just  as 
much  radiant  caloric  as  they  receive  from  it,  and  no 
change  of  temperature  will  result  from  these  equal 
interchanges. 

But  in  respect  to  the  disk  A,  as  that  is  colder  than 
the  ball  of  the  thermoscope,  it  returns  to  it  a  smaller 
quantity  of  radiant  caloric  than  it  receives  from  it ; 
consequently  the  thermoscope  receives  continually  less 
than  it  gives  :  it  would  of  course  be  gradually  exhausted 
of  caloric  and  become  colder  were  it  not  for  the  com- 
pensation it  receives  for  this  loss  from  the  disk  B.  This 
disk,  being  hotter  than  the  thermoscope,  gives  to  it 
continually  more  radiant  caloric  than  it  receives  from 
it ;  and  were  it  not  for  the  simultaneous  loss  of  caloric 
which  the  instrument  sustains  in  its  interchanges  with 
the  cold  disk  A,  its  quantity  of  caloric  would  be  aug- 
mented, and  it  would  become  hotter. 

Now,  as  the  temperature  of  the  ball  of  the  thermo- 
scope is  an  arithmetical  mean  between  that  of  the  disk 
A  and  that  of  the  disk  B,  it  is  reasonable  to  suppose 
that  the  thermoscope  receives  just  as  much  more  caloric 
from  B  than  it  gives  to  it  as  it  gives  to  A  more  than  it 
receives  from  it ;  and  if  that  be  the  case  in  fact,  it  is  evi- 
dent that  the  simultaneous  actions  of  the  two  disks  on 
the  ball  of  the  thermoscope  (or  the  traffic  which  they 
carry  on  with  it  in  caloric)  can  neither  tend  to  increase 
nor  to  diminish  the  original  stock  of  that  substance  be- 


122      Inquiry  concerning  tfie  Nature  of  Heat, 

longing  to  that  instrument ;  consequently  the  instru- 
ment will  neither  be  heated  nor  cooled  by  these  inter- 
changes, but  will  continue  invariably  at  the  same  con- 
stant temperature. 

This  explanation  is  plausible,  but,  before  the  hypoth- 
esis on  which  it  is  founded  can  be  admitted,  we  must 
see  if  it  will  agree  with  the  results  of  other  experi- 
ments, —  for  the  greatest  care  ought  always  to  be  used  in 
the  admission  of  hypotheses  in  physical  researches,  and 
in  no  case  can  it  be  more  indispensably  necessary  than 
where  an  hypothesis  has  evidently  been  contrived  for 
the  sole  purpose  of  explaining  a  single  experiment,  or 
elucidating  a  new  fact. 

When  the  surface  of  the  metallic  disk  B  was  black- 
ened by  holding  it  over  the  flame  of  a  candle,  the  in- 
tensity of  its  radiation  at  the  given  temperature  (that 
of  112°)  was  found  to  be  very  considerably  increased; 
and  when  (being  so  blackened)  it  was  again  presented 
to  the  ball  of  the  thermoscope  at-  the  same  distance  as 
in  the  last-mentioned  experiment,  and  the  cold  disk  A 
(at  the  temperature  of  32°)  was  placed  opposite  to  it  at 
an  equal  distance,  as  represented  in  Fig.  5,  the  thermo- 
scope, instead  of  continuing  to  retain  its  original  tem- 
perature (that  of  72°),  was  now  gradually  heated. 

There  is  nothing,  it  is  true,  in  that  event,  which  ap- 
pears difficult  to  explain  on  the  assumed  principles;  for, 
if  the  quantity  of  radiant  caloric  emitted  by  the  disk  B 
be  increased  by  blackening  its  surface,  the  quantity  re- 
ceived from  it  by  the  ball  of  the  thermoscope  must  be 
increased  also,  and  that  additional  quantity  must,  of 
course,  tend  to  raise  the  temperature  of  the  instrument. 
But  here  is  an  experiment  which  cannot  be  explained  on 
those  principles. 


and  the  Mode  of  its  Communication          123 

The  surface  of  the  cold  disk  A  having  been  black- 
ened as  well  as  that  of  the  hot  disk  B,  when  both  disks 
(blackened)  were  again  presented  at  equal  distances  to 
the  ball  of  the  thermoscope,  as  represented  in  Fig.  6,  it 
was  found  that  the  original  temperature  of  the  thermo- 
scope remained  unchanged. 

The  result  of  this  most  interesting  experiment  proves 
that  the  ball  of  the  thermoscope  was  just  as  much 
cooled  by  the  influence  of  the  cold  blackened  disk  as  it 
was  heated  by  the  hot  blackened  disk. 

Now,  as  it  was  found  by  experiment  that  the  intensity 
of  the  radiation  of  the  disk  B  was  increased 'by  the  black- 
ening of  the  surface  of  that  disk,  we  must  conclude 
that  the  intensity  of  the  radiation  of  the  disk  A  was 
likewise  increased  by  the  use  of  the  same  means  ;  but  if 
those  radiations  be  caloric,  emitted  by  those  bodies 
(which  the  hypothesis  in  question  supposes),  how  did  it 
happen  that  the  ball  of  the  thermoscope,  instead  of  being 
more  heated  by  the  additional  quantity  of  caloric  which 
it  received  in  consequence  of  the  blackening  of  the  disk 
A,  was  actually  more  cooled? 

It  may  perhaps  be  said  by  the  advocates  for  the  hy- 
pothesis in  question,  that  the  blackening  of  the  surface 
of  the  disk  A  caused  a  greater  quantity  of  caloric  to  be 
sent  off  to  it  by  the  ball  of  the  thermoscope.  Without 
insisting  on  an  explanation  of  the  mode  of  action  of  the 
cause  which  is  supposed  to  produce  this  effect  (which  I 
might  certainly  do,  as  the  supposition  is  perfectly  gra- 
tuitous), I  will  content  myself  with  just  observing  that 
as  the  surface  of  the  opposite  disk  was  also  blackened, 
this  supposed  augmentation  of  the  q.uantity  of  caloric 
emitted  by  the  ball  of  the  thermoscope,  occasioned  by 
the  blackening  of  the  surfaces  of  the  bodies  presented  to  it, 


1 24      Inquiry  concerning  the  Nature  of  Heat, 

can  be  of  no  use  in  explaining  the  phenomena  in  ques- 
tion. 

The  results  of  the  two  last  mentioned  experiments 
appear  to  me  to  be  very  important ;  and  I  do  not  see 
how  they  can  be  reconciled  with  the  opinions  of  modern 
chemists  respecting  the  nature  of  heat. 

In  order  to  simplify  our  speculations  on  this  ab- 
struse subject,  we  have  hitherto  supposed  that  difference 
of  temperature  depends  solely  on  the  difference  of  the 
times  of  the  vibrations  of  the  component  particles  of 
bodies.  It  is  possible,  however,  and  even  probable, 
that  it  depends  principally  on  the  'velocities  of  those 
particles ;  for  it  is  easy  to  perceive  that,  the  more  rapid 
the  motions  of  those  particles  are,  the  greater  their  elon- 
gations must  be  in  their  vibrations,  and  the  more,  of 
course,  will  the  volume  of  the  body  they  compose  be 
expanded. 

It  is  well  known  that  the  pulsations  occasioned  in  an 
elastic  fluid  by  the  vibrations  of  an  elastic  solid  body 
proceed  from  that  body  in  all  directions,  and  that  these 
pulsations  are  everywhere  (that  is  to  say,  at  all  distances 
from  the  body)  isochronous  with  the  vibrations  of  the 
solid  body  ;  it  is  known,  also,  that  the  mean  velocity  of 
any  individual  particle  of  the  fluid  is  less  in  proportion 
as  the  distance  of  the  particle  is  greater  from  the  centre 
from  which  these  pulsations  proceed. 

In  the  case  of  the  pulsations  occasioned  in  the  air  by 
the  vibrations  of  sonorous  bodies,  those  pulsations  are 
everywhere  isochronous  with  the  vibrations  of  the  sono- 
rous body,  and  the  time,  or  frequency,  of  these  pulsa- 
tions, determines  the  note ;  but  it  is  the  velocity  of  the 
particles  of  the  air,  or  the  breadth  of  the  wave,  on 
which  the  force  or  strength  of  the  sound  depends ;  and 


and  the  Mode  of  its  Communication.         125 

this  velocity  becoming  less  as  the  distance  from  the 
sonorous  body  increases,  the  sound  is  weakened  in  the 
same  proportion. 

There  are  several  circumstances  which  might  lead  us 
to  suspect  that  colour  depends  on  the  frequency  of  those 
pulsations  which  have  been  supposed  to  constitute 
light ;  and  that  the  heat  produced  by  them  is  in  pro- 
portion to  their  force. 

If  this  supposition  should  be  well  founded,  a  knowl- 
edge of  that  important  fact  might  perhaps  enable  us  to 
explain  several  very  interesting  phenomena,  —  the  com- 
bustion of  inflammable  bodies,  for  instance,  and  the  great 
intensity  of  the  heat  which  is  produced  by  the  concen- 
tration of  calorific  rays. 

There  are  several  well-known  experiments  with  burn- 
ing-glasses which  show  that  the  intensity  of  the  heat 
generated  by  the  concentration  of  the  solar  rays  is  not 
simply  as  the  condensation  of  those  rays,  but  in  a  higher 
proportion ;  and  that  it  depends  much  on  their  direc- 
tion^ being  greater  as  the  angle  is  greater  at  which  they 
meet  at  the  focus  of  the  lens. 

That  fact  is  certainly  very  remarkable.  It  has  often 
been  the  subject  of  my  meditations,  and  it  has  contrib- 
uted not  a  little  to  the  opinion  I  have  been  induced  to 
adopt  respecting  the  nature  of  light  and  of  heat.  I 
never  could  reconcile  it  with  the  supposition  that  heat 
is  caused  by  the  accumulation  of  anything  emitted  by  the 
sun,  or  by  any  other  body  which  sends  off  calorific 
radiations. 

Reserving  for  a  future  communication  an  account 
of  the  sequel  of  my  inquiries  respecting  the  subject 
which  I  have  undertaken  to  investigate,  I  shall  conclude 
this  long  paper  with  some  observations  concerning  the 


126      Inquiry  concerning  the  Nature  of  Heat, 

practical  uses  that  may  be  derived  from  a  knowledge  of 
the  facts  which  have  been  established  by  the  results  of 
the  foregoing  experiments. 

In  all  cases  where  it  is  designed  to  -preserve  the  heat 
of  any  substance  which  is  confined  in  a  metallic  vessel, 
it  will  greatly  contribute  to  that  end  if  the  external  sur- 
face of  the  vessel  be  very  clean  and  bright ;  but  if  the 
object  be  to  cool  anything  quickly  in  a  metallic  vessel, 
the  external  surface  of  the  vessel  should  be  painted,  or 
covered  with  some  of  those  substances  which  have  been 
found  to  emit  calorific  rays  in  great  abundance. 

Polished  tea-urns  may  be  kept  boiling  hot  with  a 
much  less  expense  of  spirit  of  wine  (burnt  in  a  lamp 
under  them)  than  such  as  are  varnished ;  and  the  cleaner 
and  brighter  the  dishes  and  covers  for  dishes  are  made, 
which  are  used  for  bringing  victuals  on  the  table,  and 
for  keeping  it  hot,  the  more  effectually  will  they  answer 
that  purpose. 

Saucepans  and  other  kitchen  utensils  which  are  very 
clean  and  bright  on  the  outside  may  be  kept  hot  with  a 
smaller  fire  than  such  as  are  black  and  dirty ;  but  the 
bottom  of  a  saucepan  or  boiler  should  be  blackened,  in 
order  that  its  contents  may  be  made  to  boil  quickly,  and 
with  a  small  expense  of  fuel. 

When  kitchen  utensils  are  used  over  a  fire  of  sea-coal 
or  of  wood,  there  will  be.  no  necessity  for  blackening 
their  bottoms,  for  they  will  soon  be  made  black  by  the 
smoke ;  but  when  they  are  used  over  a  clear  fire  made 
with  charcoal,  it  will  be  advisable  to  blacken  them,  — 
which  may  be  done  in  a  few  moments  by  holding  them 
over  a  wood  or  coal  fire,  or  over  the  flame  of  a  lamp  or 
candle. 

Proposals  have  often  been  made  for  constructing  the 


and  the  Mode  of  its  Communication.          127 

broad  and  shallow  vessels  (flats),  in  which  brewers  cool 
their  wort,  of  metal,  on  a  supposition  that  the  process 
of  cooling  would  go  on  faster  in  a  metallic  vessel  than 
in  a  wooden  vessel  ;  but  this  would  not  be  found  to  be 
the  case  in  fact,  a  metallic  surface  being  ill  calculated 
for  expediting  the  emission  of  calorific  rays. 

The  great  thickness  of  the  timber  of  which  brewers' 
flats  are  commonly  made  is  a  circumstance  very  favour- 
able to  a  speedy  cooling  of  the  wort ;  for,  when  the  flats 
are  empty,  this  mass  of  wet  wood  is  much  cooled,  not 
only  by  the  cold  air  which  passes  over  it,  but  also  and 
more  especially  by  evaporation  ;  and  when  the  flat  is 
again  filled  with  hot  wort  a  great  part  of  the  heat  of 
that  liquid  is  absorbed  by  the  cold  wood. 

In  all  cases  where  metallic  tubes  filled  with  steam  are 
used  for  warming  rooms  or  for  heating  drying-rooms, 
the  external  surface  of  those  tubes  should  be  painted  or 
covered  with  some  substance  which  facilitates  the  emis- 
sion of  calorific  rays.  A  covering  of  thin  paper  will 
answer  that  purpose  very  well,  especially  if  it  be  black, 
and  if  it  be  closely  and  firmly  attached  to  the  surface  of 
the  metal  with  glue. 

Tubes  which  are  designed  for  conveying  hot  steam 
from  one  place  to  another  should  either  be  well  cov- 
ered up  with  warm  covering  or  should  be  kept  clean 
and  bright.  It  would,  I  am  persuaded,  .be  worth  while, 
in  many  cases,  to  gild  them,  or  at  least  to  cover  them 
with  what  is  called  gilt  paper,  or  with  tin  foil,  or  some 
other  metallic  substance  which  does  not  easily  tarnish 
in  the  air. 

The  cylinders  and  principal  steam-tubes  of  steam- 
engines  might  be  covered  first  with  some  warm  cloth- 
ing, and  then  with  thin  sheet  brass  kept  clean  and 


128      Inquiry  concerning  the  Nature  of  Heat, 

bright.  The  expense  of  this  covering  would,  I  am  con- 
fident, be  amply  repaid  by  the  saving  of  heat  and  fuel 
which  would  result  from  it. 

If  garden  walls  painted  black  acquire  heat  faster  when 
exposed  to  the  sun's  direct  rays  than  when  they  are  not 
so  painted,  they  will  likewise  cool  faster  during  the 
night;  and  gardeners  must-  be  best  able  to  determine 
whether  these  rapid  changes  of  temperature  are,  or  are 
not,  favourable  to  fruit-trees. 

Black  clothes  are  well  known  to  be  very  warm  in  the 
sun  ;  but  they  are  far  from  being  so  in  the  shade,  and 
especially  in  cold  weather.  No  coloured  clothing  is  so 
cold  as  black  when  the  temperature  of  the  air  is  below 
that  of  the  surface  of  the  skin,  and  when  the  body  is 
not  exposed  to  the  action  of  calorific  rays  from  other 
substances. 

It  has  been  shown  that  the  warmth  of  clothing  de- 
pends much  on  the  polish  of  the  surface  of  the  substance 
of  which  it  is  made;  and  hence  we  may  conclude  that, 
in  choosing  the  colour  of  our  winter  garments,  those 
dyes  should  be  avoided  which  tend  most  to  destroy  that 
polish ;  and,  as  a  white  surface  reflects  more  light  than 
an  equal  surface,  equally  polished,  of  any  other  colour, 
there  is  much  reason  to  think  that  white  garments  are 
warmer  than  any  other  in  cold  weather.  They  are  uni- 
versally considered  as  the  coolest  that  can  be  worn  in 
very  hot  weather,  and  especially  when  a  person  is  ex- 
posed to  the  direct  rays  of  the  sun  ;  and  if  they  are  well 
calculated  to  reflect  calorific  rays  in  summer,  they  must 
be  equally  well  calculated  to  reflect  those  frigorific  rays 
by  which  we  are  cooled  and  annoyed  in  winter. 

I  have  found,  by  direct  and  decisive  experiments  (of 
which  an  account  will  hereafter  be  given  to  this  Soci- 


and  the  Mode  of  its  Communication.         129 

ety),  that  garments  of  fur  are  much  warmer  in  cold 
weather  when  worn  with  the  fur  or  hair  outwards  than 
when  it  is  turned  inwards.  Is  not  this  a  proof  that  we 
are  kept  warm  by  our  clothing,  not  so  much  by  confin- 
ing our  heat  as  by  keeping  off  those  frigorific  rays  which 
tend  to  cool  us  ? 

The  fine  fur  of  beasts,  being  a  highly  polished  sub- 
stance, is  well  calculated  to  reflect  those  rays  which  fall 
on  it ;  and  if  the  body  were  kept  warm  by  the  rays 
which  proceed  from  it  being  reflected  back  upon  it, 
there  is  reason  to  think  that  a  fur  garment  would  be 
warmest  when  worn  with  the  hair  inwards ;  but  if  it 
be  by  reflecting  and  turning  away  the  frigorific  rays 
from  external  (colder)  bodies  that  we  are  kept  warm  by 
our  clothes  in  cold  weather,  we  might  naturally  expect 
that  a  pelisse  would  be  warmest  when  worn  with  the 
hair  outwards,  as  I  have  found  it  to  be  in  fact. 

The  point  here  in  question  is  by  no  means  a  matter 
of  small  importance;  for  until  the  principles  of  the 
warmth  of  clothing  be  understood,  we  shall  not  be  able 
to  take  our  measures  with  certainty,  and  with  the  least 
possible  trouble  and  expense,  for  defending  ourselves 
against  the  inclemencies  of  the  seasons,  and  making 
ourselves  comfortable  in  all  climates. 

The  fur  of  several  delicate  animals  becomes  white  in 
winter  in  cold  countries,  and  that  of  the  bears  which 
inhabit  the  polar  regions  is  white  in  all  seasons.  These 
last  are  exposed  alternately,  in  the  open  air,  to  the  most 
intense  cold  and  to  the  continual  action  of  the  sun's 
direct  rays  during  several  months.  If  it  should  be  true 
that  heat  and  cold  are  excited  in  the  manner  above  de- 
scribed, and  that  white  is  the  colour  most  favourable  to 
the  reflection  of  calorific  and  frigorific  rays,  it  must  be 

VOL.  II.  9 


1 30      Inquiry  concerning  the  Nature  of  Heat. 

acknowledged,  even  by  the  most  determined  sceptic, 
that  these  animals  have  been  exceedingly  fortunate  in 
obtaining  clothing  so  well  adapted  to  their  local  circum- 
stances. 

The  excessive  cold  which  is  known  to  reign,  in  all 
seasons,  on  the  tops  of  very  high  mountains  and  in  the 
higher  regions  of  the  atmosphere,  and  the  frosts  at  night 
which  so  frequently  take  place  on  the  surface  of  the 
plains  below  in  very  clear  and  still  weather  in  spring 
and  autumn,  seem  to  indicate  that  frigorific  rays  arrive 
continually  at  the  surface  of  the  earth  from  every  part 
of  the  heavens. 

May  it  not  be  by  the  action  of  these  rays  that  our 
planet  is  cooled  continually,  and  enabled  to  preserve  the 
same  mean  temperature  for  ages,  notwithstanding  the 
immense  quantities  of  heat  that  are  generated  at  its  sur- 
face, by  the  continual  action  of  the  solar  rays  ? 

If  this  conjecture  should  be  well  founded,  we  should 
be  led  to  conclude  that  the  inhabitants  of  certain  hot 
countries  who  sleep  at  night  on  the  tops  of  their  houses, 
in  order  to  be  more  cool  and  comfortable,  do  wisely  in 
choosing  that  situation  to  pass  their  hours  of  rest. 

[This  paper  is  printed  from  the  Philosophical  Transactions  of  the 
Royal  Society,  XCIV.  (1804),  pp.  77  -  182.] 


EXPERIMENTAL   INVESTIGATIONS 
CONCERNING    HEAT 

SECTION  I.  —  Short  Account  of  a  new  Experiment  on  Heat. 

I  HAVE  lately  made  a  new  experiment,  the  result 
of  which  appears  to  me  sufficiently  interesting  to 
deserve  the  attention  of  the  Class. 

Having  found,  by  experiments  often  repeated,  that 
metallic  bodies,  exposed  in  the  free  air  of  a  large  apart- 
ment, are  much  more  speedily  heated  and  cooled  when 
their  surfaces  have  been  blackened  (over  the  flame  of  a 
candle,  for  example)  than  when  they  are  clean  and  pol- 
ished, I  was  curious  to  know  whether  the  same  phe- 
nomena would  take  place  when,  instead  of  exposing 
these  bodies  in  the  open  air,  they  should  be  placed  in 
close  metallic  vessels,  surrounded  by  a  certain  thickness 
of  included  air,  and  these  vessels  should  be  then  plunged 
in  a  large  mass  of  hot  or  cold  water.  In  order  to  clear 
up  this  important  point,  I  made  the  following  experi- 
ment :  — 

A  cylindrical  vessel  of  brass,  three  inches  in  diame- 
ter and  four  inches  long,  was  enclosed  in  another  larger 
cylindrical  vessel,  in  the  centre  of  which  it  was  sus- 
pended by  its  neck,  so  as  to  touch  it  in  no  other  part, 
leaving  on  all  sides  an  interval  of  one  inch  between  the 
vessels. 

The  external  vessel,  as  well  as  the  smaller  one  in- 
cluded within  it,  is  made  of  thin  sheets  of  brass;  its 


132  Experimental  Investigations 

diameter  is  five  inches,  and  its  height  six.  It  is  one 
inch  and  a  half  in  diameter,  and  six  inches  high.  Its 
neck  is  one  inch  and  a  quarter  in  diameter,  and  two 
inches  and  a  half  long. 

The  interior  vessel  is  suspended  in  the  centre  of  the 
external  one  by  a  stopper  of  cork.  This  stopper  is 
adjusted  to  the  neck  of  the  external  vessel,  and  there  is 
a  cylindrical  hole  of  three  quarters  of  an  inch  diameter 
through  the  cork,  and  having  the  same  axis  ;  which  per- 
foration receives  the  neck  of  the  interior  vessel,  and 
retains  it  in  its  place. 

The  interior  vessel  was  introduced  and  fixed  in  its 
place  before  the  bottom  of  the  exterior  vessel  was  sol- 
dered in. 

At  the  centre  of  the  bottom  of  the  great  vessel  is  a 
small  metallic  tube,  of  three  quarters  of  an  inch  diame- 
ter and  one  inch  and  a  half  long,  by  means  of  which 
this  instrument  is  attached  to  a  solid  heavy  foot  of 
metal,  which  supports  it  in  'a  vertical  position  when  the 
whole  instrument  is  submerged  in  a  vessel  of  water. 

This  instrument,  which  greatly  resembles  that  de- 
scribed in  my  seventh  Essay  on  the  Propagation  of 
Heat  in  Fluids,  which  I  have  called  the  passage  ther- 
mometer* may  be  used  to  make  a  number  of  interesting 
experiments  on  the  cooling  of  bodies  through  different 
fluids.  In  the  present  experiment  I  employed  it  in  the 
following  manner  :  — 

The  interior  vessel  was  entirely  filled  with  hot  water 
to  the  height  of  half  an  inch  in  its  neck,  and  a  good 
thermometer,  having  its  cylindrical  bulb  four  inches 
long,  was  inserted  therein.  The  instrument  was  then 
plunged  in  a  mixture  of  pounded  ice  and  water,  and 

*  See  Vol.  I.  p.  237. 


concerning  Heat,  133 

the  time  was  noted  by  means  of  the  thermometer, 
during  which  the  hot  water  in  the  small  vessel  became 
cold. 

I  was  careful  to  plunge  the  instrument  in  this  frigo- 
rific  mixture,  so  that  the  large  vessel  was  completely 
submerged,  except  the  upper  extremity  of  its  neck ;  and 
I  added,  from  time  to  time,  a  sufficient  quantity  of 
pounded  ice  to  keep  the  frigorific  mixture  constantly 
and  throughout  at  the  temperature  of  melting  ice. 

The  following  were  the'  results  afforded  by  two  simi- 
lar instruments,  employed  at  the  same  time  :  — 

These  two  instruments,  which  I  shall  distinguish 
respectively  by  the  letters  A  and  B,  are  of  the  same 
form  and  dimensions ;  there  is  no  difference  between 
them  but  in  the  state  of  their  surfaces.  In  the  instru- 
ment A  the  exterior  surface  of  the  small  vessel  and  the 
interior  surface  of  the  great  vessel  which  encloses  it 
are  bright  and  polished ;  but  in  the  instrument  B 
the  exterior  surface  of  the  small*  vessel  and  the  inte- 
rior surface  of  the  large  vessel  are  black,  having  been 
blackened  over  the  flame  of  a  candle,  before  the  bottom 
of  the  great  vessel  was  soldered  in  its  place. 

Having  filled  the  interior  vessel  of  each  of  these  in- 
struments with  boiling  water  till  the  water  rose  to  the 
height  of  half  an  inch  in  the  neck,  I  placed  a  ther- 
mometer in  each  ;  and  then  plunging  both  instruments 
at  the  same  time  into  a  tub  filled  with  cold  water,  mixed 
with  pounded  ice,  I  observed  the  course  of  their  refrig- 
eration during  several  hours. 

Each  of  the  instruments  was  completely  submerged 
in  the  frigorific  mixture,  excepting  about  one  inch  of  the 
superior  extremity  of  the  neck  of  the  exterior  vessel, 
and  I  was  careful  to  add  new  quantities  of  pounded  ice, 


134  Experimental  Investigations 

from  time  to  time,  in  order  to  keep  the  frigorific  mix- 
ture constantly  at  the  precise  temperature  of  melting  ice. 

As  the  specific  gravity  of  water  at  the  temperature  of 
three  or  four  degrees  of  the  thermometer  of  Reaumur 
is  greater  than  that  of  melting  ice,  the  water  which  lies 
at  the  bottom  of  a  vessel  containing  a  mixture  of  water 
and  pounded  ice  is  usually  warmer  than  the  fluid  which 
occupies  the  upper  part  of  the  vessel.  To  remedy  this 
inconvenience,  my  refrigeratory  for  the  frigorific  mixture 
was  a  tin  vessel,  supported  on 'three  feet  of  one  inch  in 
length;  and  I  placed  this  first  vessel  in  a  larger  one  of 
wood,  containing  a  certain  quantity  of  ice  surrounding 
the  bottom  and  part  of  the  sides  of  the  metallic  vessel. 

As  in  the  first  moments  of  the  experiment  the  ther- 
mometers descended  too  quickly  to  be  observed  with 
precision,  I  waited  till  each  of  them  had  arrived  at  the 
55th  degree  of  Reaumur  ;  after  which  I  carefully  ob- 
served the  number  of  minutes  and  seconds  employed  in 
passing  through  each  interval  of  five  degrees  of  the  lower 
part  of  the  scale  of  the  thermometer  to  the  fifth  degree 
above  zero. 

Degrees  of  the  Time  employed  in  cooling 

thermometer.  By  the  instrument  A.  By  the  instrument  B 


From 

55  to 

50   .  '   . 

1  1 

6 

•  .  :  •'••    •  7 

5° 

" 

50  « 

45 

13 

'5 

8 

"10 

" 

45  " 

40  . 

•  15 

12 

.    .  9 

5 

" 

40  " 

35 

19 

10 

10 

5° 

" 

35  " 

30  . 

.   22 

24 

.  12 

18 

" 

30  « 

25 

27 

5° 

.    15 

to 

M 

•7  r  " 

/T 

1  5 

« 

2O  " 

'5 

54 

15 

28 

" 

15  « 

10 

.  80 

25 

V   .   .   .  4« 

25 

" 

10  " 

5    •  • 

.   183 

45 

.   .   .    85 

15 

Time   employed   in    cooling |       g 
from  55°  to  5°,  j  47 


254    5 


concerning  Heat. 


135 


The  foregoing  table  exhibits  the  depression  of  the 
thermometers  during  eight  hours  employed  in  the  ex- 
periment. 

It  is  evident,  from  the  results  of  this  experiment, 
that  the  blackened  body  is  constantly  cooled  in  less 
time  than  the  polished  body ;  but  it  appears,  by  the 
course  of  the  thermometers,  that  the  difference  between 
the  quickness  of  cooling  of  these  two  bodies  varies, 
and  that  this  difference  was  less  considerable  in  propor- 
tion as  the  temperature  of  the  bodies  was  more  elevated 
in  comparison  to  that  of  the  medium  in  which  they  were 
exposed  to  cool. 

In  cooling  from  the  55th  degree  to  the  5oth  above 
the  temperature  of  the  surrounding  medium,  the  pol- 
ished body  employed  1 1  minutes  and  6  seconds,  and 
the  blackened  body  employed  7  minutes  and  50  sec- 
onds to  pass  through  the  same  interval.  But  from  the 
loth  to  the  1 5th  degree  above  the  temperature  of  the 
medium,  the  polished  body  employed  183  minutes  and 
45  seconds,  while  the  blackened  body  employed  only  85 
minutes  and  15  seconds;  but  it  is  extremely  probable 
that  this  difference  between  the  proportion  of  the  times 
employed  in  cooling  the  two  bodies  at  different  tem- 
peratures is  only  apparent,  and  that  it  depends  on  the 
greater  or  less  time  required  for  the  thermometers  in 
the  vessels  to  arrive  at  the  mean  temperatures  of  th«» 
masses  of  water  which  surround  them. 

In  order  to  compare  the  results  of  this  experiment 
with  those  I  made  last  year  with  metallic  vessels,  pol- 
ished and  blackened,  and  left  to  cool  in  the  undisturbed 
air  of  a  large  chamber,  it  is  necessary  to  ascertain  how 
much  time  the  two  bodies  in  question  employed  in  cool- 
ing from  the  5oth  to  the  4Oth  degree  of  Fahrenheit 


136  Experimental  Investigations 

above  the  temperature  of  the  medium.  Now,  I  found, 
by  observation,  that  the  polished  vessel  A  employed 
39  minutes  and  30  seconds  to  pass  over  that  interval 
of  cooling,  while  the  blackened  vessel  B  employed  only 
11  minutes.  These  times  are  in  the  proportion  of 
10,000  to  5810.  By  one  of  my  experiments,  made  last 
year,  I  found  that  the  times  employed  in  passing  through 
the  same  interval  of  cooling  in  the  open  air  by  a  clean 
polished  metallic  vessel,  and  another  of  the  same  form 
and  capacity,  but  blackened  without,  were  as  10,000  to 

5654- 

Reflecting  on  the  consequences  which  ought  to  result 
from  the  radiations  of  bodies,  on  the  supposition  that 
the  temperatures  of  bodies  are  always  changing  by 
means  of  these  radiations,  I  was  led  to  the  following 
conclusion  :  If  the  intensity  of  the  action  of  the  rays 
which  proceed  •  from  a  body  be  universally  as  the 
squares  of  the  distances  of  bodies  inversely,  which  is 
extremely  probable,  a  hot  body  exposed  to  cool  in  a 
close  place,  or  surrounded  on  all  sides  by  walls,  ought 
to  cool  with  the  same  celerity,  or  in  the  same  time, 
whatever  may  be  the  magnitude  of  this  enclosure,  pro- 
vided the  temperature  of  the  sides  or  walls  be  at  a 
constant  given  temperature;  and  the  results  of  the 
experiment  here  described,  in  which  the  hot  body  was  en- 
closed in  a  vessel  of  a  few  inches  diameter,  compared  with 
those  of  several  experiments  made  last  year,  in  which 
the  heated  bodies  were  exposed  to  cool  between  the  walls 
of  a  large  chamber,  appear  to  confirm  this  conclusion. 

As  to  the  effect  produced  by  the  air  in  cooling  a 
heated  body  exposed  to  cool  in  a  close  place  filled  with 
that  fluid,  I  have  reason  to  believe  that  it  is  much  less 
considerable  than  has  been  supposed. 


concerning  Heat.  137 

I  have  shown,  by  direct  and  conclusive  experiments, 
that  bodies  cool  and  are  heated,  and  that  with  consider- 
able celerity,  when  placed  in  a  space  void  of  air ;  * 
and  by  experiments  made  last  year,  with  the  intention 
of  clearing  up  this  point,  I  found  reasons  to  conclude 
that  when  a  hot  body  cools  in  tranquil  air,  not  agitated 
by  winds,  one  twenty-seventh  only  of  the  heat  lost  by 
this  body  (or,  to  speak  more  correctly,  which  it  excites 
in  surrounding  bodies)  is  communicated  to  the  air, 
all  the  rest  being  carried  to  a  distance  through  the  air 
and  communicated  by  radiation  to  the  surrounding  solid 
bodies. 

SECTION  II.  —  Experiments  on  cooling  Bodies. 

It  is  only  by  careful  observation  of  the  phenomena 
which  accompany  the  heating  and  cooling  of  bodies, 
that  we  can  hope  to  acquire  exact  notions  of  the  nature 
of  heat  and  its  manner  of  acting. 

Many  experiments  have  been  made  by  different  per- 
sons, at  different  times,  with  a  view  to  determine  what 
has  been  called  the  conducting  quality  of  different  sub- 
stances with  regard  to  heat.  I  have  myself  made  a  con- 
siderable number ;  and  it  is  from  their  results,  often  no 
less  unexpected  than  interesting,  that  I  have  been  gradu- 
ally led  to  adopt  the  opinions  on  the  nature  of  heat  which 
I  have  presumed  to  submit  to  the  judgment  of  this 
illustrious  assembly.  The  flattering  attention  with 
which  the  Class  has  honoured  the  three  Memoirs  I 
have  lately  presented  encourages  me  to  communicate  the 
continuation  of  my  researches. 

All  philosophers  are  agreed  in  considering  glass  as 
one  of  the  worst  conductors  of  heat  which  exists  ;  and 

*  In  my  Essay  on  the  Propagation  of  Heat  in  various  Substances.     See  Vol.  I. 
p.  401. 


138  Experimental  Investigations 

when  it  is  proposed  to  confine  the  heat  in  a  body,  of 
which  the  temperature  has  been  raised,  or  to  hinder  its 
dissipation  as  much  as  possible,  care  is  taken  to  sur- 
round the  heated  body  with  substances  known  to  be 
bad  conductors  of  heat. 

The  results  of  many  of  my  experiments  having  led 
me  to  suspect  that  the  cooling  of  bodies  is  not  effected 
in  the  manner  which  is  generally  supposed,  I  made  the 
following  experiment,  with  the  intention  of  clearing  up 
this  interesting  part  of  the  science. 

I  procured  two  bottles,  nearly  cylindrical,  of  the  same 
form  and  the  same  dimensions  when  measured  exter- 
nally, —  one  being  of  glass,  and  very  thick,  and  the 
other  of  tin  or  tinned  iron,  which  was  very  thin.  Each 
of  them  is  three  inches  ten  lines  in  diameter,  very 
nearly,  and  five  inches  in  height ;  and  each  has  a  neck 
one  inch  three  lines  in  diameter,  and  one  inch  two  lines 
in  height.  The  glass  bottle  weighs  13  ounces,  i  gros, 
and  1 8  grains  poids  de  marc;  and  the  other  thin  me- 
tallic vessel  weighs  only  5  ounces,  i  gros,  and  65  grains. 

Having  very  exactly  weighed  the  bottle  of  tinned 
iron,  I  found  its  exterior  surface  to  be  54.462  inches, 
which  give  0.21142  of  a  line  for  the  thickness  of 
its  sides,  taking  the  specific  gravity  of  the  metal  ac 
7.8404. 

The  mean  thickness  of  the  sides  of  the  glass  bottle 
is  more  than  six  times  as  great,  as  may  be  easily  de- 
duced from  a  calculation  founded  on  the  weight  of  the 
bottle,  the  quantity  of  its  surface,  and  the  specific  grav- 
ity of  glass. 

Having  filled  these  two  bottles  with  boiling  water, 
I  hung  them  up  by  slender  strings  in  the  midst  of 
the  tranquil  air  of  a  large  chamber,  at  the  height  of 


concerning  Heat.  139 

five  feet  from  the  floor,  and  at  the  distance  of  four  feet 
asunder. 

The  temperature  of  the  air  of  the  chamber,  which 
did  not  vary  a  quarter  of  a  degree  during  the  .whole 
time  of  the  experiment,  was  9!  degrees  of  Reaumur's 
scale. 

An  excellent  mercurial  thermometer,  with  a  cylindri- 
cal bulb,  of  four  inches  long  and  two  lines  and  a  half 
in  diameter,  suspended  in  the  axis  of  each  of  these 
bottles,  indicated  the  temperature  of  the  contained 
water  ;  and  the  time  employed  in  its  cooling  for  every 
five  degrees  of  Fahrenheit's  thermometer  was  carefully 
observed,  during  eight  hours. 

The  glass  being  considered  as  a  very  bad  conductor 
of  heat,  and  the  sides  of  the  bottle  being  so  thick,  who 
would  not  have  expected  that  the  water  in  this  bottle 
would  have  been  more  slowly  cooled  than  that  in  the 
very  thin  bottle  of  tin  ? 

The  contrary,  however,  was  the  event ;  the  bottle 
of  glass  was  cooled  almost  twice  as  quickly  as  that  of 
tin. 

While  the  water  included  in  the  bottle  of  tinned 
iron  employed  56  minutes  to  pass  through  a  cer- 
tain interval  of  cooling,  —  namely,  through  ten  degrees, 
between  the  5oth  and  4Oth  degree  of  the  thermometer 
of  Fahrenheit  above  the  temperature  of  the  air  of  the 
chamber,  —  the  water  in  the  glass  bottle  employed  only 
30  minutes  for  the  same  change. 

It  appears  to  me  that  the  result  of  this  experiment 
throws  great  light  on  the  mysterious  operation  of  the 
communication  of  heat. 

If  we  admit  the  hypothesis  that  hot  bodies  are 
cooled,  not  by  losing  or  acquiring  some  material  sub- 


140          .       Experimental  Investigations 

stance,  but  by  the  action  of  colder  surrounding  bodies, 
communicated  by  undulations  or  radiations  excited  in 
an  ethereal  fluid,  the  results  of  this  experiment  may 
be  easily  explained ;  but,  if  this  hypothesis  be  not 
adopted,  I  cannot  explain  them. 

It  might,  perhaps,  be  suspected  that  the  air  attached 
by  a  certain  attraction,  but  with  unequal  forces,  to  the 
surfaces  of  the  two  bottles,  might  have  been  the  cause 
of  this  remarkable  difference  in  the  time  of  their  cool- 
ing ;  but  those  who  will  take  the  trouble  to  reflect 
attentively  on  the  results  of  the  experiments  I  have 
described  in  a  preceding  Memoir,  which  were  made  with 
a  view  to  clear  up  this  point,  with  a  metallic  vessel  first 
naked,  and  afterwards  with  one,  two,  four,  and  five  coat- 
ings of  varnish,  will  be  persuaded  that  this  cause  is  not 
sufficient  to  explain  the  facts. 

By  a  course  of  experiments  made  at  Munich,  last 
year,  of  which  the  details  are  given  in  a  Memoir  sent  to 
the  Royal  Society  of  London,*  I  have  found  that  a 
given  quantity  of  hot  water,  included  in  a  metallic  ves- 
sel of  a  given  form  and  capacity,  always  cools  with  the 
same  quickness  in  the  air,  whatever  may  be  the  metal 
employed  to  construct  the  vessel ;  provided  always  that 
the  external  surface  of  the  vessel  be  very  clean,  and  the 
temperature  of  the  air  the  same. 

In  order  that  the  cooling  shall  be  effected  in  the  same 
time,  nothing  more  is  required  than  that  the  external 
surface  of  the  vessel  be  truly  metallic,  and  not  covered 
with  oxide,  or  other  foreign  bodies. 

On  the  inquiry,  what  quality  all  the  metals  might 
have  in  common,  and  possess  in  the  same  degree,  to 
which  this  remarkable  equality  of  their  susceptibil- 

*  See  p.  23. 


concerning  Heat.  141 

ity  of  cooling  might  be  attributed,  I  found  it  in  their 
opacity. 

The  rays  which  cannot  penetrate  the  surface  of  a 
body  must  necessarily  be  thrown  back,  or  reflected ; 
and  as  the  rays  of  light,  which  have  much  analogy  with 
the  invisible  calorific  or  frigorific  rays,  easily  penetrate 
glass,  though  they  are  reflected,  at  least  for  the  greatest 
part,  by  metallic  surfaces,  I  suspected  beforehand  the 
result  of  the  experiment  with  the  two  bottles,  —  one  of 
glass,  and  the  other  of  tinned  iron. 

The  state  of  a  heated  body,  or  a  body  which  con- 
tains a  certain  quantity  of  caloric,  has  been  compared 
to  that  of  a  sponge  which  contains  a  certain  quantity  of 
water.  Supposing  this  comparison  to  be  just,  we  might 
compare  the  loss  of  heat  by  the  emission  of  the  ca- 
lorific rays  to  the  loss  of  water  by  evaporation.  Let 
us  try  if  this  comparison  can  supply  us  with  the  means 
of  throwing  some  light  on  the  interesting  subject  of  our 
researches. 

Instead  of  the  sponge  filled  with  water,  let  us  substi- 
tute the  earth,  and  suppose,  for  a  moment,  that  the 
earth  is  everywhere  equally  heated,  and  its  surface,  in 
all  parts,  covered  with  a  bed  of  the  same  kind  of  soil, 
equally  moist. 

As  a  square  league  in  a  mountainous  country  contains 
more  surface,  or  more  superficial  acres  than  a  square 
league  situated  in  the  plain,  it  is  evident  that  more 
water  would  be  evaporated  from  the  whole  surface  of 
the  earth  in  a  given  time,  if  the  earth  were  covered  with 
mountains  than  if  its  surface  were  an  immense  plain, 
and,  consequently,  that  more  caloric  ought  to  be  pro- 
jected from  the  surface  of  any  solid  body  broken  with 
asperities,  than  from  the  surface  of  another  body,  of  the 


142  Experimental  Investigations 

same  form  and  dimensions,  which  is  smooth  or  well 
polished. 

This  reasoning  appears  to  me  to  be  just,  and,  if  I 
am  not  deceived,  the  conclusions  which  may  be  drawn 
from  the  facts  in  question,  well  confirmed  by  experi- 
ment, ought  to  be  considered  as  demonstrative.  I 
have  taken  every  possible  care  to  establish  these  facts  ; 
and  the  results  of  all  my  experiments  have  constantly 
shown  that  more  or  less  perfect  polish,  or  the  greater  or 
less  brightness  of  the  surface  of  a  metallic  vessel,  does 
not  sensibly  influence  the  time  of  its  cooling. 

I  took  two  equal  vessels  of  brass,  and  polished  the 
external  surface  of  one  of  them  as  highly  as  possible  ; 
and  I  destroyed  the  polish  of  the  other  by  rubbing  it 
in  all  directions  with  coarse  emery.  When  these  two 
vessels  were  filled  with  hot  water,  I  did  not  find  that 
the  unpolished  vessel  employed  more  or  less  time  in 
cooling  than  that  which  was  polished. 

I  was  careful  to  wash  the  surface  of  the  unpolished 
vessel  effectually  with  water,  before  the  experiment ;  as 
I  knew  that  if  I  did  not  take  the  precaution  of  remov- 
ing all  the  dirt  which  might  be  lodged  in  the  asperities 
of  the  surface,  the  presence  of  these  small  foreign  bod- 
ies would  influence  the  result  of  the  experiment  in  a 
sensible  manner. 

We  ought  carefully  to  distinguish  those  surfaces 
which  appear  unpolished  to  our  eyes,  but  which  in 
fact  are  not  so,  from  those  which  reflect  little  or  no 
light. 

It  is  more  than  probable  that  the  surface  of  a  metal 
is  always  polished,  and  even  always  equally  so  in  all  the 
cases  wherein  the  metal  is  naked  and  clear  and  clean, 
notwithstanding  all  the  mechanical  means  which  may 


concerning  Heat.  143 

be  used  to  scratch  its  surface  and  break  the  glare  of  its 
lustre. 

Let  us  return  to  the  comparison  of  the  evaporation 
of  water  from  the  surface  of  the  earth,  with  the  emis- 
sion of  caloric  radiating  from  the  surface  of  a  heated 
body,  and  let  us  suppose,  for  an  instant,  that  the  evapo- 
ration of  the  water  from  the  surface  of  the  earth  does 
not  depend  on  the  heat  of  the  earth  itself,  but  that  it  is 
caused  merely  by  the  influences  of  surrounding  bodies, 
—  as,  for  example,  by  the  rays  of  light  received  from 
the  sun.  It  is  evident  that,  in  this  case,  the  evapora- 
tion could  not  be  sensibly  greater  in  a  mountainous 
country  than  in  the  plain ;  and  by  an  easy  analogy  we 
see  that  if  hot  bodies  be  cooled,  not  in  consequence  of 
the  emission  of  some  material  substance  from  their  sur- 
faces, but  by  the  positive  action  of  rays  sent  to  them 
by  colder  surrounding  bodies,  the  more  or  less  perfect 
polish  of  their  surfaces  ought  not  sensibly  to  influence 
the  rapidity  of  their  cooling. 

This  is  precisely  what  all  my  experiments  concur  to 
prove. 

I  have  long  sought,  and  with  that  patience  which  the 
love  of  the  sciences  inspires,  to  reconcile  the  results  of 
my  experiments  with  the  opinions  generally  received 
concerning  the  nature  of  heat  and  its  mode  of  action, 
but  without  being  able  to  succeed. 

It  is  in  the  hands  of  two  of  the  most  illustrious 
bodies  of  learned  men  that  ever  existed  that  I  have 
thought  it  incumbent  on  me  to  deposit  my  labours,  my 
discoveries,  my  doubts,  and  my  conjectures. 

I  am  earnestly  desirous  of  engaging  the  philosophers 
of  all  countries  to  turn  their  attention  towards  an  ob- 
ject of  inquiry  too  long  neglected. 


144  Experimental  Investigations 

The  science  of  heat  is  not  only  of  great  curiosity,  from 
the  multitude  of  astonishing  phenomena  it  offers  to  our 
contemplation,  but  it  is  likewise  extremely  interesting 
from  its  intimate  connection  with  all  the  useful  arts,  and 
generally  with  all  the  mechanical  occupations  of  human 
life. 

Without  a  knowledge  of  heat,  it  is  not  possible  either 
to  excite  it  with  economy  or  to  direct  its  different  opera- 
tions with  facility  and  precision. 

SECTION  III.  —  Experiments  tending  to  show  that  Heat  is 
communicated  through  solid  Bodies,  by  a  Law  which 
is  the  same  as  that  which  would  ensue  from  Radiation 
between  the  Particles. 

Having  made  a  considerable  number  of  experiments 
on  the  passage  of  heat  through  fluids,  and  through  dif- 
ferent substances  in  the  state  of  powder,  I  was  curious 
to  ascertain  the  laws  of  its  propagation  through  solid 
bodies,  particularly  metals. 

I  hoped  this  discovery  would  furnish  some  additional 
data  to  confirm  or  refute  the  opinions  I  had  adopted 
concerning  heat  and  its  manner  of  acting ;  and  it  will 
be  seen  by  the  results  that  my  expectations  were  not 
frustrated. 

Having  procured  two  cylindrical  vessels  of  tin,  each 
six  inches  in  diameter  and  six  inches  high,  I  fastened 
them  together,  by  means  of  a  solid  cylinder  of  copper, 
six  inches  long  and  an  inch  and  a  half  in  diameter, 
which  was  fixed  horizontally  between  the  two  tin  ves- 
sels. The  extremities  of  the  cylinder  passed  through 
two  holes,  an  inch  and  a  half  in  diameter,  made  for 
the  purpose  in  the  sides  of  the  vessels,  midway  be- 


concerning  Heat.  145 

tween  the  bottom  and  top,  and  were  soldered  fast  in 
them. 

Each  of  the  vessels  was  made  flat  on  the  side  where 
the  copper  cylinder  was  fastened,  so  that  the  extremity 
of  the  cylinder  did  not  project  into  the  vessel,  but  was 
level  with  the  flattened  part. 

This  instrument  was  supported  at  the  height  of  eight 
inches  and  a  half  above  the  table  on  which  it  stood,  by 
means  of  three  feet,  —  two  fixed  to  one  of  the  vessels, 
and  one  to  the  other. 

One  of  these  vessels  being  filled  with  boiling  water, 
the  other  with  water  at  the  freezing  point,  as  the  two 
extremities  of  the  cylinder  were  placed  in  immediate 
contact  with  these  two  masses  of  fluid,  a  change  of 
temperature  must  necessarily  take  place  by  degrees  in 
all  the  interior  parts  of  the  cylinder.  For  the  pur- 
pose of  observing  this  change,  three  vertical  holes  were 
made  in  the  cylinder,  into  which  were  introduced  the 
bulbs  of  three  small  mercurial  thermometers.  One 
of  the  holes  was  in  the  middle  of  the  cylinder,  the 
others  midway  between  the  centre  and  either  extrem- 
ity. 

Each  of  these  holes  is  four  lines  in  diameter,  and 
eleven  lines  and  a  half  deep ;  so  that  the  bulbs  of  the 
thermometers,  which  are  three  lines  in  diameter,  were 
all  in  the  axis  of  the  cylinder. 

When  the  thermometers  were  put  in  their  places,  the 
holes  were  filled  with  mercury,  in  order  to  facilitate  the 
communication  of  heat  from  the  metal  to  the  bulb  of 
the  thermometer. 

To  keep  the  hot  water  constantly  boiling,  a  spirit- 
lamp  was  placed  beneath  the  vessel  containing  it;  and 
to  keep  the  cold  water  constantly  at  the  temperature  of 


146 


Experimental  Investigations 


melting  ice,  fresh  portions  of  ice  were  added  to  it,  from 
time  to  time. 

The  thermometers  are  graduated  to  Fahrenheit's 
scale,  the  freezing  point  being  marked  32°,  and  that  of 
boiling  water  212°. 

As  the  first  and  most  important  object  I  had  in  view 
was  to  learn  at  what  temperature  the  three  thermome- 
ters would  become  stationary,  I  did  not  very  carefully 
notice  the  progress  of  the  thermometers  toward  this 
point ;  but  as  soon  as  they  appeared  nearly  stationary, 
I  observed  them  with  the  greatest  attention  for  near 
half  an  hour. 

To  distinguish  the  three  thermometers,  I  shall  call 
that  nearest  the  boiling  water  B,  that  in  the  centre  C, 
and  that  nearest  the  cold  water  D. 

The  following  are  the  progress  and  results  of  an  ex- 
periment made  the  28th  of  April,  1804,  the  tempera- 
ture of  the  air  being  78°  of  Fahrenheit. 


Time. 

Temperature 
of  the  hot  water. 

Temperature 
marked  by  the 
thermometer  B. 

Temperature 
marked  by  the 
thermometer  C. 

Temperature 
marked  by  the 
thermometerD. 

Temperature  of 
the  cold  water. 

h.      m.      s. 

Degrees. 

Degrees. 

Degrees. 

Degrees. 

Degrees. 

I       52    15 

212 

1  60 

130 

J05 

32 

—  53  30 



160^ 

131 

i°5£ 



—  55 



161 

ttt| 

1  06 



—  56  3° 



I6i| 

I32 

io6| 



—  58 



162 

134 

107 



2          O       O 



162 

I32f 

107^ 



—       I     30 



162 

133 

l°?i 



—    4 



162 

»3*l 

io6| 



—    6 

— 

162 

132 

1  06 



—    9 



162 

I32| 

ic6£ 



—  ii 



162 

I32j 

io6£ 



—  28 



162 

i3£f 

t*| 



Before  I  proceed  to  examine  more  minutely  the  re- 
sults of  this    experiment,    I.  will    endeavour    to    show 


concerning  Heat.  147 

those  results  which  it  ought  to  have  exhibited,  on  the 
supposition  that  heat  is  propagated,  even  in  the  interior 
of  solid  bodies,  by  radiations  emanating  from  the  sur- 
faces of  the  particles  composing  these  bodies. 

On  this  supposition,  we  must  necessarily  consider 
the  particles  that  compose  bodies  as  being  separate  from 
each  other.,  and  even  by.  pretty  considerable  distances, 
compared  with  the  diameters  of  these  particles ;  but 
there  is  nothing  repugnant  to  the  admission  of  this  sup- 
position ;  on  the  contrary,  there  are  many  phenomena 
which  apparently  indicate  that  all  the  solid  bodies  with 
which  we  are  acquainted  are  thus  formed. 

To  see  now  by  what  law  heat  would  be  propagated 
in  a  solid  cylinder,  let  us  represent  the  axis  of  this  cylin- 
der by  a  right  line  A  E,  Plate  IV.  Fig.  i  ;  and  let 
us  begin  with  supposing  that  the  cylinder  consists  of 
three  particles  of  matter  only,  ACE,  placed  at  equal 
distances  in  that  line. 

Let  us  farther  suppose  that  the  extremity,  A,  of  the 
cylinder  is  constantly  at  the  temperature  of  boiling  water, 
while  its  other  extremity,  E,  remains  invariably  at  the 
freezing  point. 

By  an  experiment,  of  which  I  have  already  given  an 
account  to  the  Class,*  I  found  that  when  two  equal 
bodies,  A  B,  one  hotter  than  the  other,  are  isolated  and 
placed  opposite  each  other,  the  intensities  of  their  ra- 
diations are  such,  that  a  third  body,  C,  placed  in  the 
middle  of  the  space  that  separates  them,  will  acquire  a 
temperature,  by  the  simultaneous  action  of  these  ra- 
diations, which  will  be  an  arithmetical  mean  between 
those  of  the  two  bodies  A  and  B. 

From  the  result  of  this  experiment  we  have  ground 

*  See  the  preceding  paper. 


148  Experimental  Investigations 

to  conclude  that  if  the  cylinder  were  composed  of  three 
particles  of  matter  only,  A,  C,  E,  the  particle  C,  which 
is  in  the  middle  of  the  cylinder,  must  necessarily  have 
the  arithmetical  mean  temperature  between  that  of  A 
and  that  of  E,  which  are  at  the  two  extremities  of  the 
cylinder;  that  is  to  say,  between  212°  and  32°  of  Fah- 
renheit, which  is  122°. 

Now  let  us  interpose  between  the  particles  A,  C,  and 
E,  two  other  particles,  B,  D,  and  see  whether  the  intro- 
duction of  these  two  particles  will  make  any  change  in 
the  temperature  of  the  particle  C  that  occupies  the  mid- 
dle of  the  cylinder. 

If  the  particle  B  be  placed  in  the  middle  of  the  space 
comprised  between  the  extremity,  A,  of  the  cylinder  and 
its  middle,  C,  it  ought  to  acquire  a  mean  temperature 
between  that  of  the  extremity,  A,  of  the  cylinder,  and 
that  of  the  point  C,  namely  that  of  167°,  the  mean  be- 
tween 212°  and  122°;  and  if  the  particle  D  be  placed  in 
the  midst  of  the  space  comprised  between  the  middle 
of  the  cylinder  and  its  other  extremity,  E,  this  particle 
ought  to  acquire  a  mean  temperature  between  that  of 
the  middle  of  the  cylinder  and  that  of  its  extremity,  E  ; 
it  ought  then  to  have  the  temperature  of  77°. 

From  this  new  arrangement,  the  particle  C,  situate 
in  the  middle  of  the  cylinder,  will  find  for  its  neigh- 
bours, on  one  side  the  particle  B,  at  the  temperature  of 
167°,  and  on  the  other  the  particle  D,  at  that  of  77°. 
The  point  in  question  is,  whether  the  presence  of  these 
two  particles  will  make  any  change  in  the  temperature 
of  the  particle  C,  or  not. 

In  the  first  place,  it  is  evident  that  if  the  calorific  in- 
fluences of  the  particle  B  on  the  particle  C  be  as  effica- 
cious in  heating  it  as  the  frigorific  influences  of  the 


concerning  Heat.  149 

particle  D  be  in  cooling  it,  the  temperature  of  the  particle 
C  ought  not  to  be  changed.  But  experience  has  shown 
that,  at  equal  distances  and  equal  intervals  of  tempera- 
ture, the  calorific  influences  of  hot  bodies  and  the  frigo- 
rific  influences  of  cold  bodies  are  exactly  equal ;  and  as 
the  distance  from  B  to  C  is  equal  to  the  distance  from 
D  to  C,  while  the  interval  of  temperature  between  B 
and  C,  =  45°,  is  the  same  as  that  between  D  and  C, 
=  45°,  it  is  evident  that  the  temperature  of  the  par- 
ticle C,  which  is  in  the  middle  of  the  cylinder,  can  be 
no  way  affected  by  the  introduction  of  the  intermediate 
particles  B  and  D. 

By  the  same  way  of  reasoning  may  be  proved,  that 
the  introduction  of  an  indefinite  number  of  interme- 
diate particles  would  produce  no  change  in  the  tempera- 
ture of  the  middle  of  the  axis  of  the  cylinder,  or  in  any 
part  of  it;  and  if  the  introduction  of  an  indefinite  num- 
ber of  intermediate  particles  make  no  change  in  the  state 
of  a  thermometer  placed  in  the  middle  of  the  axis  of 
the  cylinder,  we  may  conclude  that  the  thermometer 
would  remain  equally  stationary  if  the  number  of  inter- 
mediate particles  were  increased  till  they  had  that  prox- 
imity to  each  other  which  is  necessary  to  constitute  a 
solid  body.  If,  instead  of  a  single  row  of  particles  in  a 
right  line,  there  were  a  bundle  composed  of  an  indefinite 
number  of  such  rows  placed  side  by  side,  forming  a 
solid  cylinder,  the  temperature  in  the  different  parts  of 
the  line  A  E  would  remain  the  same. 

From  this  reasoning  we  may  infer  that  the  tempera- 
tures of  the  different  parts  of  the  cylinder  should  de- 
crease in  arithmetical  progression  from  one  extremity 
of  the  cylinder  to  the  other. 

But  it  is  evident  that  this  law  of  decrement  of  tern- 


150  Experimental  Investigations 

perature  could  take  place  only  in  the  single  case  of  the 
surface  of  the  cylinder  being  completely  isolated,  so  as 
to  be  no  way  affected  by  the  action  of  surrounding 
bodies,  which  is  absolutely  impossible. 

The  circumstances  under  which  the  experiments  were 
made  are  very  different  from  those  here  taken  for 
granted.  The  bodies  we  subject  to  experiment  are  con- 
stantly surrounded  on  all  sides  by  the  air  and  other 
bodies  which  act  on  our  instruments  continually,  and 
often  in  a  very  perceptible  manner ;  and  we  can  never 
hope  to  isolate  a  cylinder  so  completely  that  the  appar- 
ent progress  of  heat  in  its  interior  shall  perceptibly 
obey  the  law  we  have  just  discovered.  In  common 
cases  it  deviates  widely  from  this  law. 

As  the  causes  of  this  deviation  are  well  known,  we 
will  see  whether  there  be  no  means  of  appreciating  their 
effects. 

The  surface  of  the  cylinder  being  surrounded  by  the 
atmospheric  air  and  other  bodies,  all  which  are  of  a 
known  and  sensibly  constant  temperature,  we  may  de- 
termine the  comparative  effects  of  these  bodies  on  the 
different  parts  of  the  surface  of  the  cylinder. 

In  those  parts  of  the  cylinder  which  are  hotter  than 
the  air  and  other  surrounding  bodies,  the  surface  of  the 
cylinder  will  be  cooled  by  the  action  of  these  bodies ; 
but  if  one  of  the  extremities  of  the  cylinder  be  colder 
than  the  atmospheric  air,  those  parts  of  the  cylinder 
which  are  colder  than  the  circumambient  fluid  will  be 
heated  by  its  influence  and  that  of  the  surrounding 
bodies. 

We  will  begin  with  examining  the  case  where  the 
coldest  extremity  of  the  cylinder  is  at  the  same  tem- 
perature as  the  surrounding  air.  Let  us  suppose, 


concerning  Heat.  151 

then,  that  the  experiment  with  boiling  water  at  the  one 
end  and  freezing  at  the  other  be  made  when  the  tem- 
perature of  the  air  is  at  the  freezing  point,  or  32°  of 
Fahrenheit. 

In  this  case  it  is  evident  that  the  surface  of  the  cyl- 
inder must  everywhere  be  cooled  by  the  influence  of  the 
surrounding  atmosphere.  The  question,  then,  is  to 
determine  the  comparative  effects,  or  the  relative  quan- 
tities of  refrigeration  or  loss  of  heat,  that  must  take 
place  in  the  different  farts  of  the  cylinder  ;  and,  in  the  first 
place,  it  is  clear  that  the  hotter  a  given  part  of  the  cyl- 
inder is,  the  more  heat  it  must  lose  in  a  given  time,  by 
the  influence  of  the  surrounding  cold  bodies;  whence 
we  may  conclude  that  the  refrigeration  of  the  surface  of 
the  cylinder  by  the  influence  of  the  air  and  other  sur- 
rounding cold  bodies  must  necessarily  diminish  from 
the  extremity  of  the  cylinder,  A,  which  is  in  contact  with 
the  hot  water,  to  its  extremity,  E,  which  is  in  contact 
with  the  cold. 

From  reasoning  which  appears  incontrovertible,  and 
which  the  results  of  a  great  number  of  experiments 
appear  to  confirm,  it  has  been  concluded  that  the  celer- 
ity with  which  a  hot  body  placed  in  a  cold  medium  is 
cooled  is  always  proportional  to  the  difference  between 
the  temperature  of  the  hot  body  and  that  of  the  me- 
dium. Considering  this  conclusion  as  established,  we 
may  determine  a  •priori  what  ought  to  be  the  gradation 
of  temperatures  in  the  interior  of  a  given  solid  cylinder 
surrounded  by  air,  one  extremity  of  which  is  in  contact 
with  a  considerable  body  of  boiling  water,  while  the 
other  is  similarly  in  contact  with  cold. 

We  have  seen  that,  if  the  surface  of  the  cylinder  were 
perfectly  isolated,  the  decrease  of  temperature  from  the 


152  Experimental  Investigations 

hottest  extremity  of  the  cylinder,  A,  to  its  other  extrem- 
ity, E,  which  is  in  contact  with  cold  water,  would  be  in 
arithmetical  progression^  and  it  has  just  been  shown  that 
the  decrease  must  necessarily  be  accelerated  by  the  ac- 
tion of  the  air  and  other  surrounding  cold  bodies. 

But  the  acceleration  of  the  decrease  of  temperature  in 
those  parts  of  the  cylinder  which  are  toward  the  cold 
extremity,  depending  on  the  action  of  the  air  and  sur- 
rounding bodies,  must  be  continually  diminishing  in 
proportion  as  the  temperature  of  the  surface  of  the  cyl- 
inder approaches  nearer  and  nearer  that  of  the  air  ;  and 
hence  we  may  conclude  that,  if  a  given  number  of  points, 
at  equal  distances  from  each  other,  be  taken  in  the  axis 
of  the  cylinder,  the  temperatures  corresponding  with 
these  points  will  be  in  geometrical  progression. 

We  may  represent  the  progress  of  the  decrease  of 
temperature  by  Plate  IV.  Fig.  2. 

In  a  right  line  A  E,  representing  the  axis  of  the  cylin- 
der, if  we  take  the  three  points  B,  C,  and  D,  so  that 
the  distances  A  B,  B  C,  C  D,  and  D  E  shall  be  equal, 
and,  erecting  the  perpendiculars  A  F,  B  G,  C  H,  D  I, 
EK,  take  A  F  =  the  temperature  of  the  cylinder  at 
its  extremity  A,  B  G  =  its  temperature  at  the  point  B, 
and  so  of  the  rest;  the  ordinates  A  F,  B  G,  &c.  will 
be  in  geometrical  progression,  while  their  corresponding 
abscisses  are  in  arithmetical  progression ;  consequently 
the  curve,  P  Q,  which  touches  the  extremities  of  all 
these  ordinates,  must  necessarily  be  the  logarithmic  curve. 

We  will  now  see  whether  the  results  of  experiment 
agree  with  the  theory  here  exhibited,  or  not. 

To  form  our  judgment  with  ease  and,  as  it  were,  at  a 
single  glance,  of  the  agreement  of  our  theory  with  the 
results  of  the  experiment  of  which  I  gave  an  account 


concerning  Heat.  153 

at  the  beginning  of  this  Memoir,  we  have  only  to  repre- 
sent these  results  by  a  figure  in  the  following  manner. 

On  the  horizontal  line  A  E,  Fig.  3,  representing  the 
axis  of  the  cylinder  employed  in  the  experiment,  we  will 
take  three  points,  B,  C,  and  D  ;  one,  C,  in  the  middle 
of  the  axis,  being  the  situation  of  the  central  thermom- 
eter, the  other  two,  B  and  D,  at  the  intermediate  points 
which  the  other  two  thermometers  occupied  between 
the  middle  of  the  axis  and  its  two  extremities. 

Erecting  the  perpendiculars  A/,  B  gy  C  /z,  D  /,  and 
E  k,  on  the  points  A,  B,  C,  D,  and  E ;  and  taking  the 
ordinate  Af=  212,  the  temperature  of  boiling  water, 
B  g  =  162,  the  temperature  indicated  by  the  thermom- 
eter B,  C  h  =  132!,  the  temperature  indicated  by 
the  thermometer  C,  D  /  =  io6-|,  the  temperature  given 
by  the  thermometer  D,  and  lastly,  E  k  =  32,  the  tem- 
perature of  water  mixed  with  pounded  ice, — a  curve, 
P  Q,  passing  through  the  points  /,  g,  h,  i,  k,  ought  to 
be  the  logarithmic;  that  is,  supposing  the  temperature 
of  the  surrounding  air  to  be  constantly  at  the  tempera- 
ture of  melting  ice  during  the  experiment. 

But  the  experiment  in  question  was  made  when  the 
temperature  of  the  air  was  at  78°  F. ;  consequently, 
reckoning  from  a  certain  point,  taken  in  the  length  of 
the  cylinder,  where  the  temperature  was  at  78°,  to  the 
extremity,  E,  the  influence  of  the  surrounding  air,  in- 
stead of  cooling  the  surface  of  the  cylinder,  heated  it ;  and 
it  is  evident  that  the  curve,  P  Q,  must  necessarily  in  this 
case  have  a  point  of  inflection. 

In  fact,  it  appears  on  a  simple  inspection  of  the  figure, 
that  the  curve,  P  Q,  has  a  point  of  inflection  ;  but  we  see, 
likewise,  that  this  curve  is  not  regular.  That  branch 
which  is  concave  toward  the  axis  of  the  cylinder  is  not 


154  Experimental  Investigations 

similar  to  the  adjoining  portion  of  the  curve,  of  equal 
length,  which  is  convex  toward  that  axis,  as  it  ought  to 
be  according  to  our  theory ;  and  even  the  part  of  the 
curve  which  is  convex  toward  the  axis,  A  E,  differs  sen- 
sibly from  the  logarithmic,  particularly  toward  its  ex- 
tremity, P. 

It  ought  necessarily  to  differ  from  this  curve  as  far 
as  the  divisions  of  our  thermometers  are  defective ;  but  the 
deviation  between  the  ordinates,  A  /and  B  g,  indicated 
by  the  results  of  the  experiment  in  question,  appears  to 
me  much  too  considerable  to  be  ascribed  to  the  imper- 
fection of  our  thermometers. 

To  see  how  far  the  curve,  P  Q,  differs  from  the  loga- 
rithmic, we  have  only  to  draw  a  logarithmic  curve,  R  S, 
through  the  points  g  and  /,  and  we  shall  find,  that  the 
ordinates  corresponding  to  the  points 

A,  B,  C,  D,  E, 

o  o  o  o  o 

Instead  of  being       212.00          162          132^          io6j         32.00 
Will  be  199-55         J6z         131  io6£         86.35 

Difference  — I2-45  °  — 'i  °        +54-35 

The  very  great  difference  that  exists  between  the  tem- 
perature of  cold  water  and  that  indicated  by  the  results 
of  the  experiment  for  the  extremity  of  the  cylinder 
which  was  in  contact  with  this  water  led  me  to  suspect 
that  it  was  owing  to  the  quality  possessed  by  water  in 
common  with  other  fluids,  which  renders  it  a  very  bad 
conductor  of  heat. 

If  it  be  true,  as  I  believe  I  have  elsewhere  proved, 
that  there  is  no  sensible  communication  of  heat  be- 
tween the  adjacent  particles  of  a  fluid,  from  one  to 
another,  and  that  heat  is  propagated  through  fluids 
only  in  consequence  of  a  motion  of  their  particles,  re- 


concerning  Heat,  155 

suiting  from  a  change  in  their  specific  gravity,  occa- 
sioned by  their  being  heated  or  cooled ;  as  the  specific 
gravity  of  water  is  very  little  altered  by  an  inconsidera- 
ble change  of  temperature  when  this  fluid  is  near  the 
freezing  point,  it  might  have  been  foreseen  that  a  solid 
body  a  little  heated,  and  plunged  into  cold  water,  would 
be  very  slowly  cooled. 

The  result  of  the  following  experiment,  which  I 
made  with  a  view  to  elucidate  this  point,  will  put  the 
fact  out  of  all  doubt. 

The  three  thermometers  being  stationary,  one,  B,  at 
162°,  the  second,  C,  at  ijsf0,  and  the  third,  D,  at 
io6J°,  the  water  in  contact  with  one  of  the  extremities 
of  the  cylinder  being  still  boiling,  while  the  water  mixed 
with  pounded  ice,  which  was  in  contact  with  the  other 
extremity,  was  constantly  at  the  temperature  of  melting 
ice,  I  began  to  stir  this  mixture  of  ice  and  water  pretty 
briskly  with  a  little  stick,  and  I  continued  to  stir  it 
uninterruptedly  and  with  the  same  velocity  for  22 
minutes. 

I  had  scarcely  begun  this  operation  when  I  had  a 
proof  that  my  conjectures  were  well  founded.  The 
mercury  in  the  three  thermometers  immediately  began 
to  descend,  and  did  not  stop  till  it  had  fallen  very  con- 
siderably. 

The  thermometer  B  fell  from  162°  to  152°;  C  from 
132!°  to  inf°;  and  D  from  io6J°  to  78}°. 

On  comparing  these  numbers,  we  find  that,  in  con- 
sequence of  the  agitation  of  the  cold  water  for  22 
minutes,  the  thermometer  B  fell  10°  of  Fahrenheit's 
scale,  the  thermomete  C  21°,  and  the  thermometer  D 
28°. 

As  soon  as   I   had  ceased  to  stir  the  cold  water  the 


156  Experimental  Investigations 

three  thermometers  began  to  rise,  and  at  the  end  of  a 
quarter  of  an  hour  they  had  all  reached  the  points  from 
which  they  set  out  at  the  beginning  of  this  operation. 

To  facilitate  the  comparison  of  the  results  of  these 
two  experiments,  —  one  made  with  cold  water  at  rest,  the 
other  with  the  same  water  in  a  state  of  constant  agita- 
tion, —  I  have  represented  them  in  Fig.  4. 

In  the  first  place,  we  shall  learn  several  very  interest- 
ing facts  by  simple  inspection  of  this  figure ;  we  shall 
see,  — 

i  st.  That  the  progress  of  refrigeration  —  or,  to  speak 
more  properly,  the  decrease  of  temperature  —  was  every- 
where much  more  rapid  when  the  cold  water  in  contact 
with  the  extremity,  E,  of  the  cylinder  was  agitated  than 
when  it  was  at  rest. 

2dly.  That  the  extremity  of  the  cylinder  in  contact 
with  this  water  was  constantly  near  jo°  colder  'in  the 
first  case  than  in  the  second. 

^dly.  We  shall  see  that  the  progress  of  refrigeration 
was  everywhere,  and  in  both  the  experiments,  such 
nearly  as  our  theory  points  out. 

The  decrease  of  temperature  toward  the  middle  of  the 
cylinder  was  so  regular  that  it  is  more  than  probable 
the  apparent  irregularities  toward  the  two  extremities 
were  occasioned  solely  by  the  difficulty  which  a  body  of 
water  finds  in  communicating  its  mean  temperature  to 
a  solid  with  which  it  is  in  contact. 

The  boiling  water  being  in  continual  motion,  owing 
to  its  ebullition,  it  had  a  great  advantage  over  the  cold 
water,  which  was  at  rest,  in  communicating  its  tempera- 
ture to  the  extremity  of  the  cylinder  it  touched;  but  I 
have  found,  notwithstanding  this,  that  by  agitating  the 
boiling  water  strongly  with  a  quill,  and  particularly 


concerning  Heat.  157 

when  with  the  quill  I  made  a  rapid  friction  against  the 
end  of  the  cylinder  immersed  in  the  boiling  water,  I 
occasioned  all  the  thermometers  to  rise  several  degrees. 

It  may  perhaps  be  imagined,  at  first  sight  of  the  re- 
sults of  the  experiment,  that  as  the  three  thermometers, 
which  occupied  the  parts  about  the  middle  of  the  axis 
of  the  cylinder,  did  not  indicate  a  decrease  perfectly 
agreeing  with  the  theory,  the  theory  itself  cannot  be 
true ;  but  a  moment's  reflection  will  show  that  this  in- 
ference would  be  too  hasty,  and  that  the  difference  be- 
tween the  theory  and  the  results  of  our  experiments,  far 
from  proving  anything  adverse  to  the  theory,  serve  on 
the  contrary  to  render  it  more  probable. 

The  results  of  such  experiments  can  never  agree  with 
the  theory,  except  the  divisions  of  our  thermometers  be 
perfectly  accurate;  but  it  is  well  known  to  everyone 
who  has  any  knowledge  of  natural  philosophy  that  the 
divisions  of  our  thermometers  are  defective. 

One  of  the  objects  I  had  in  view  in  the  experiments 
of  which  I  have  just  given  an  account  to  the  Class,  and 
in  several  others  which  I  intend  to  make  without  delay, 
is  to  improve  the  division  of  the  scale  of  the  thermom- 
eter, in  order  to  render  this  valuable  instrument  of 
greater  utility  in  the  delicate  investigations  of  natural 
philosophy. 

It  appears  certain  that  the  increase  of  the  elasticity 
of  air  by  heat  is  much  more  nearly  proportionate  to  the 
increase  of  temperature  than  the  dilatation  of  mercury 
or  any  known  fluid  ;  consequently,  it  is  the  air  thermom- 
eter we  ought  to  endeavour  to  improve,  and  which 
must  ultimately  afford  us  the  most  accurate  measure  of 
heat  that  it  is  possible  for  us  to  procure. 


158  Experimental  Investigations 

SECTION  IV. —  The  Heat  produced  in  a  Body  by  a  given 
Quantity  of  solar  Light  is  the  same  whether  the  Rays  be 
denser  or  rarer,  convergent,  parallel,  or  divergent. 

In  all  cases  where  the  rays  of  the  sun  strike  on  the  sur- 
face of  an  opaque  body  without  being  reflected,  heat  is 
generated  and  the  temperature  of  the  body  is  increased; 
but  is  the  quantity  of  heat  thus  excited  always  in  pro- 
portion to  the  quantity  of  light  that  has  disappeared  ? 
This  is  a  very  interesting  question  and  has  not  hitherto 
found  a  decisive  solution. 

When  we  consider  the  prodigious  intensity  of  the 
heat  excited  in  the  focus  of -a  burning  mirror  or  a  lens, 
we  are  tempted  to  believe  that  the  concentration  and 
condensation  of  the  solar  rays  increase  their  power  of 
exciting  heat ;  but,  if  we  examine  the  matter  more 
closely,  we  are  obliged  to  confess  that  such  an  augmen- 
tation would  be  inexplicable.  It  would  be  equally  so 
on  both  the  hypotheses  which  natural  philosophers 
have  formed  of  the  nature  of  light ;  for  if  light  be  analo- 
gous to  sound,  since  it  has  been  proved,  both  by  calcu- 
lation and  experiment,  that  two  undulations  in  an 
elastic  fluid  may  approach  and  even  cross  each  other 
without  deranging  either  their  respective  directions  or 
velocities,  we  do  not  see  how  the  concentration  or  con- 
densation of  these  undulations  can  increase  their  force  of 
impulse;  and  if  light  be  a  real  emanation,  as  its  velocity 
is  not  altered  either  by  the  change  of  direction  it  under- 
goes in  passing  through  a  lens  or  by  its  reflection  from 
the  surface  of  a  polished  body,  it  seems  to  me  that  the 
power  of  each  of  these  particles  to  excite  or  impart 
heat  must  necessarily  be  the  same  after  refraction  or 
reflection  as  before,  and  consequently,  that  the  heat 


concerning  Heat.  159 

communicated  or  excited  must  be,  in  all  cases,  as  the 
quantity  of  light  absorbed. 

I  have  just  made  some  experiments  which  appear  to 
me  to  establish. this  fact  beyond  question. 

Having  procured  from  the  optician  Lerebours  two 
lenses  perfectly  equal,  and  of  the  same  kind  of  glass, 
4  inches  in  diameter,  and  of  nj  focus,  I  exposed  them 
at  the  same  time  to  the  sun,  side  by  side,  about  noon, 
when  the  sky  was  very  clear ;  and  by  means  of  two 
thermometers,  or  reservoirs  of  heat,  of  a  peculiar  con- 
struction, I  determined  the  relative  quantities  of  heat 
that  were  excited  in  given  times  by  the  solar  rays  at  dif- 
ferent distances  from  the  foci  of  the  lenses. 

The  two  reservoirs  of  heat  are  a  sort  of  flat  boxes  of 
brass  filled  with  water.  Each  of  these  reservoirs  is 
3  inches  ioj  lines  in  diameter,  and  6  lines  thick,  well 
polished  externally  on  all  sides  except  one  of  its  two 
flat  faces,  which  was  blackened  by  the  smoke  of  a 
candle.  On  this  face  the  solar  rays  were  received  in 
the  experiments. 

Each  of  these  reservoirs  of  heat  weighs  when  empty 
6850  grains,  folds  de  marc  (near  a  pound  troy),  and 
contains  1210  grains  of  water  (about  2  oz.  2  dwts.). 

Taking  the  capacity  of  brass  for  heat  to  be  to  that 
of  water  as  i  to  n,  it  appears  that  the  capacity  of 
the  metallic  box  weighing  6850  grains  is  equal  to  the 
capacity  of  622  grains  of  water;  and,  adding  this  quan- 
tity of  water  to  that  contained  in  the  box,  we  shall  have 
the  capacity  of  the  reservoir  prepared  for  the  experi- 
ments equal  to  that  of  1832  grains  of  water. 

Each  reservoir  is  kept  in  its  place  by  a  cylinder  of 
dry  wood,  one  of  the  extremities  of  the  cylinder  being 
fixed  in  a  socket  in  the  centre  of  the  interior  face  of  the 


160  Experimental  Investigations 

reservoir ;  and  each  reservoir  has  a  little  neck,  through 
which  it  is  filled  with  water,  and  which  after  receives 
the  bulb  of  a  cylindrical  thermometer,  that  reaches  com- 
pletely across  the  inside  of  the  box  in  the  direction  of 
its  diameter. 

The  two  reservoirs  of  heat,  with  their  two  lenses,  are 
firmly  fixed  in  an  open  frame,  which  being  movable  in 
all  directions  by  means  of  a  pivot  and  a  hinge,  the  ap- 
paratus is  easily  directed  toward  the  sun,  and  made  to 
follow  its  motion  regularly,  so  as  to  keep  the  solar 
spectra  constantly  in  the  centres  of  the  blackened  faces 
of  the  reservoirs. 

In  order  that  the  quantities  of  light  passing  through 
the  two  lenses  should  be  perfectly  equal,  a  circular  plate 
of  well-polished  brass,  in  the  centre  of  which  is  a  circu- 
lar hole  3!  inches  in  diameter,  is  placed  immediately 
before  each  of  the  lenses. 

When  the  reservoirs  of  heat  are  placed  at  different 
distances  from  the  focuses  of  their  respective  lenses,  the 
diameters  of  the  solar  spectra  which  .are  formed  on  the 
blackened  faces  of  the  reservoirs  are  necessarily  differ- 
ent ;  and  as  the  quantities  of  light  are  equal,  its  density 
at  the  surface  of  each  reservoir  is  inversely  as  the  square 
of  the  diameter  of  the  spectrum  formed  on  that  surface. 

Experiment  No.  I.  —  In  this  experiment  the  reservoir 
A  was  placed  so  near  the  focus  of  the  lens,  between 
the  lens  and  the  focus,  that  the  diameter  of  the  solar 
spectrum  falling  on  it  was  only  half  an  inch,  or  6  lines, 
while  the  reservoir  B  was  advanced  so  far  before  the 
focus  that  the  spectrum  was  2  inches  in  diameter,  or 
24  lines. 

As  the  quantities  of  light  falling  on  both  were  equal, 
the  density  of  the  light  at  the  surface  of  the  reservoir 


concerning  Heat.  161 

A  was  to  the  density  of  that  at  the  surface  of  the  reser- 
voir B  as  the  square  of  24  to  the  square  of  6,  or  as 
i 6  to  i. 

I  imagined  that  if  the  quantity  of  heat  which  a  given 
quantity  of  light  is  capable  of  exciting  depended  any 
way  on  its  density,  as  the  densities  were  so  different 
in  this  experiment,  I  could  not  fail  to  discover  the 
fact  by  the  difference  of  time  which  it  would  require 
to  raise  the  two  thermometers  the  same  number  of 
degrees. 

Having  continued  the  experiment  more  than  an  hour, 
on  a  very  fine  day,  when  the  sun  was  near  the  meridian 
and  shone  extremely  bright,  I  did  not  find  that  one  of 
the  reservoirs  was  heated  perceptibly  quicker  than  the 
other. 

Experiment  No.  2.  —  I  placed  the  reservoir  of  heat 
A  still  nearer  the  focus  of  the  lens,  in  a  situation  where 
the  solar  spectrum  was  only  4!  lines  in  diameter,  and 
where  blackened  paper  caught  fire  in  two  or  three  sec- 
onds ;  and  I  removed  the  reservoir  B  still  farther  from 
the  focus,  advancing  it  forward  till  the  diameter  of  the 
spectrum  was  2  inches  3  lines. 

The  densities  of  the  light  at  the  surfaces  of  the  reser- 
voirs in  this  experiment  were  as  32  to  i. 

The  temperature  of  the  reservoirs  as  well  as  that  of 
the  atmosphere,  at  the  beginning  of  the  experiment,  was 
54°  F.,  =  9f  R. 

The  reservoir  A,  after  having  been  exposed  to  the 
action  of  very  intense  light  near  the  focus  of  the  lens 
for  24  minutes  40  seconds,  was  raised  to  the  tempera- 
ture of  80°  F.,  =  2 if  R. 

The  reservoir  B,  which  was  much  farther  from  the 
fjcus  of  its  lens,  was  raised  to  the  same  temperature, 

VOL.  II.  II 


162 


Experimental  Investigations 


80°  F.,  a  little  more  quickly,  or  in  23  minutes  40  sec- 
onds. 

To  raise  the  temperature  of  the  reservoir  A  to  100° 
F.,  =  3of°  R.,  it  was  necessary  to  continue  the  experi- 
ment for  i  hour  15  minutes  10  seconds,  reckoning 
from  the  commencement  of  it ;  but  the  reservoir  B 
reached  the  same  temperature  in  i  hour  12  minutes  10 
seconds. 

The  progress  of  this  experiment  from  the  beginning 
to  the  end  is  exhibited  in  the  following  table. 


Time  taken. 

Increases  of 

Temperature. 

By  A. 

By  B. 

m.      s. 

m.       s. 

From  54°  to  80°  F. 

24     40 

23     40 

80          85 

7    45 

7    30 

85          90 

9    55 

9      o 

90          95 

13    30 

13      o 

95        100 

19    20 

19      o 

From  54°  to  100° 

75     10 

72    10 

This  experiment  was  begun  at  7  minutes  30  seconds 
after  n,  and  finished  at  22  minutes  40  seconds  after  12, 
the  sky  being  perfectly  clear  during  the  time. 

On  comparing  all  the  results  of  this  experiment,  we 
see  that  the  reservoir  A,  which  was  placed  very  near 
the  focus,  was  more  slowly  heated  than  the  reservoir  B, 
which  was  at  a  considerable  distance  from  it.  The  dif- 
ferences of  time,  however,  taken  to  heat  them  an  equal 
number  of  degrees  were  very  trifling,  and  I  think  may 
be  easily  explained  without  supposing  the  condensation 
of  light  to  increase  its  faculty  of  exciting  heat. 

In  both  the  preceding  experiments  the  solar  rays 
striking  on  the  reservoirs  of  heat  were  convergent,  and 
they  were  even  equally  so  on  both  sides.  To  deter- 
mine whether  •parallel  rays  have  the  same  power  of  ex- 


concerning  Heat.  163 

citing  heat  as  convergent  rays,  I  made  the  following 
experiment. 

Experiment  No.  3.  —  Having  removed  the  lens  from 
before  the  reservoir  B,  I  suffered  the  direct  rays  of  the 
sun  to  fall  on  the  blackened  face  of  the  reservoir,  through 
the  circular  hole,  3^  inches  in  diameter,  in  the  round 
brass  plate  which  had  been  constantly  placed  before  that 
lens  in  the  preceding  experiments. 

The  reservoir  A  was  placed  behind  its  lens  as  in  the 
former  experiments,  and  at  the  place  where  the  solar 
spectrum  had  6  lines  diameter. 

Having  exposed  this  apparatus  to  the  sun,  I  found 
that  the  reservoir  B,  on  which  the  direct  rays  fell,  was 
heated  sensibly  quicker  than  the  reservoir  A,  which  was 
exposed  to  the  action  of  the  concentrated  rays  near  the 
focus  of  the  lens. 

The  temperature  of  the  apparatus  and  of  the  atmos- 
phere at  the  beginning  of  the  experiment  being  53°  F., 
=  9!°  R,  the  reservoir  A  required  23  minutes  30 
seconds  to  raise  it  to  the  temperature  of  80°  F.,  =  2i|° 
R. ;  but  the  reservoir  B,  which  was  exposed  to  the 
direct  rays  of  the  sun,  acquired  the  same  temperature 
in  1 8  minutes  30  seconds. 

To  reach  the  temperature  of  100°  F.,  =  30^°  R.,  took 
the  reservoir  A  i  hour  and  3  minutes,  but  the  reser- 
voir B  47  minutes  15  seconds  only. 

The  following  table  will  show  the  progress  of  this 
experiment  from  the  beginning  to  the  end. 


164 


Experimental  Investigah 


Increases  of 

Time  taken. 

Temperature. 

By  A.                                  By  B. 

From  53°  to  65°  F. 

m.      s. 

8     26 

7      o 

65         70 

4     10 

3     15 

70          75 

5     10 

3    45 

75          8° 

5    40 

4    30 

So         85 

7      o 

4    45 

85          90 

7    3° 

5    45 

90         95 

10    30 

8      o 

95        100 

13     10 

10     15 

100        105 

20         0 

14    45 

From  53°  to  105° 

Si     36             '          62    30 

As  a  considerable  part  of  the  light  that  fell  on  the 
lens  before  the  reservoir  A  was  lost  in  passing  through 
it,  it  is  evident  that  the  quantity  received  by  this  reser- 
voir was  less  than  that  received  by  the  reservoir  B, 
which  was  exposed  to  the  direct  rays  of  the  sun  ;  and 
we  have  seen  that  the  latter  was  heated  more  rapidly 
than  the  former. 

As  we  know  not  exactly  how  much  light  was  lost  in 
passing  through  the  lens,  we  cannot  determine  from  the 
results  of  this  experiment  whether  convergent  rays  be 
more  or  less  efficacious  in  exciting  heat  than  parallel 
rays  ;  but  the  difference  in  the  times  of  heating  was  not 
greater,  as  it  appears  to  me,  than  we  might  have  ex- 
pected to  find  it,  supposing  it  to  be  occasioned  solely 
by  the  difference  between  the  quantities  of  light  acting 
on  the  reservoirs. 

The  result  of  the  following  experiment  will  establish 
this  point  beyond  doubt. 

Experiment  No.  4.  —  Having  replaced  the  lens  belong- 
ing to  the  reservoir  B,  I  adjusted  this  reservoir  to  such 
a  distance  between  the  lens  and  its  focus  that  the  solar 
spectrum  was  one  inch  in  diameter;  and  I  placed  the 
reservoir  A  at  the  same  distance  beyond  its  focus. 


concerning  Heat. 


165 


As  the  quantities  of  light  directed  toward  both  were 
equal,  and  as  the  diameters  of  the  spectra,  and  conse- 
quently the  densities  of  the  light  that  formed  them  were 
also  equal,  there  could  be  no  difference  between  the  re- 
sults of  the  experiments  with  the  two  reservoirs,  except 
what  was  occasioned  by  the  difference  in  the  direction  of 
the  rays  that  formed  the  spectra.  On  one  hand  these 
rays  were  convergent^  and  on  the  other  divergent ;  and  I 
had  inferred  that  if  parallel  rays  were  in  reality  less  effica- 
cious in  exciting  heat  than  convergent  rays,  as  some 
philosophers  have  supposed,  divergent  rays  must  be  still 
less  efficacious  than  parallel  rays,  and  consequently  much 
less  than  convergent  rays. 

Having  made  the  experiment  with  all  possible  care, 
I  found  no  sensible  difference  between  the  quantities  of 
heat  excited  in  a  given  time  by  divergent  and  convergent 
rays. 

The  following  are  the  particulars  of  the  progress  and 
results  of  this  experiment. 


Increases  of 
Heat. 

Time  taken. 

By  A, 
with  divergent  Rays. 

By  B, 
with  convergent  Rays. 

From  60°  to  65°  F. 
65         70 
70          75 
75         80 

4     5° 

4    55 
5    27 
6    13 

4     50 
5        ° 

5    25 
6    is 

From  60°  to  80° 

21      25 

21       30 

From  the  results  of  all  the  experiments  of  which  I 
have  just  given  an  account  to  the  Class,  we  may  con- 
clude that  the  quantity  of  heat  excited  or  communi- 
cated by  the  solar  rays  is  always,  and  under  all  circum- 
stances, as  the  quantity  of  light  that  disappears. 

[This  paper  is,  in  part,  printed  from  Nicholson's  Journal,  XII. 
(1805),  pp.  65 -75  and  154-171;  and  in  part  translated  from  the 
Memoires  de  1'Institut,  etc.,  VI.  (1805),  pp.  88-  133.] 


REFLECTIONS  ON    HEAT. 

THE  most  excellent  gift  which  man  has  received 
from  the  Author  of  his  being  is  the  power  which 
he  possesses  of  freeing  himself  from  the  prejudices  aris- 
ing from  the  deceptive  testimony  of  his  senses,  and  of 
penetrating  into  the  mysteries  of  Nature. 

The  animals  see  as  we  do,  without  doubt,  that  the 
sun,  moon,  and  stars  rise  and  set ;  man  in  a  state  of 
nature,  when  his  attention  is  aroused,  discovers  irregu- 
larities in  these  movements ;  the  man  of  genius,  how- 
ever, does  not  allow  himself  to  be  deceived  by  appear- 
ances, but  causes  to  come  forth  from  this  confusion  that 
vast  and  wonderful  system  of  laws  which  govern  the 
mechanism  of  the  Universe. 

The  first  step  in  science  is  to  observe  facts  attentively, 
and  in  their  proper  connection  ;  the  second  is  to  learn 
to  doubt.  The  sublime  in  science  consists  in  employ- 
ing it  to  extend  the  power  and  increase  the  innocent 
enjoyments  of  the  human  race. 

There  is  no  branch  of  the  physical  sciences  which  is 
so  intimately  connected  with  all  the  every-day  occupa- 
tions of  man  as  that  of  Heat,  and  consequently  there  is 
no  one  of  them  which  interests  him  so  closely. 

Fire  is  the  most  universal  and  active  agent  with 
which  we  are  acquainted,  and  it  is  to  the  power  which 
he  has  been  able  to  acquire  over  this  wonderful  princi- 
ple that  man  owes  the  supernatural  strength  which  has 


Reflections  on  Heat.  167 

made  him  superior  to  all  animals,  and  master  of  land 
and  sea. 

It  is  not  at  all  surprising  that  an  agent  at  once  so 
powerful  and  so  manageable,  so  beneficent  and  so  ter- 
rible, should  have  become  an  object  of  admiration  and 
even  of  adoration  among  the  nations  of  the  earth  ;  but 
it  is  more  than  surprising  that  a  subject,  the  investiga- 
tion of  which  is  of  such  interest,  should  have  been  for 
so  long  a  time  neglected. 

This  indifference  to  an  object  at  once  so  curious  and 
so  interesting  can  only  be  attributed  to  that  lack  of  at- 
tention with  which  men  always  regard  those  things  that 
they  are  accustomed  to  have  before  them  at  all  times. 

A  proof  that  our  knowledge  on  the  subject  of  heat  is 
still  extremely  limited  and  imperfect  lies  in  the  differ- 
ence of  opinion  which  exists  among  the  learned  on  the 
nature  of  heat  and  its  mode  of  action.  Some  regard  it 
as  a  substance,  others  as  a  vibratory  motion  of  the  particles 
of  matter  of  which  a  body  is  composed. 

Those  who  have  adopted  the  hypothesis  of  a  peculiar 
calorific  substance  which  they  call  caloric  suppose  that 
the  heating  of  a  body  is  always  the  result  of  an  accumu- 
lation of  this  substance  in  the  body ;  on  the  other  hand, 
those  who  regard  heat  as  a  vibratory  motion  which  is 
conceived  to  exist  always  with  greater  or  less  rapidity 
among  the  particles  of  all  bodies,  consider  heat  as  an 
acceleration  of  this  motion. 

On  the  hypothesis  of  vibratory  motion,  a  body  which 
has  become  cold  is  thought  to  have  lost  nothing  except 
motion  ;  on  the  other  hypothesis  it  is  supposed  to  have 
lost  some  material  substance,  that  is,  caloric. 

The  eminent  French  philosophers,  who  proposed, 
twenty-five  years  ago,  the  modern  hypothesis  of  caloric, 


1 68  Reflections  on  Heat. 

far  from  considering  the  existence  of  this  substance  as 
proved,  always  speak  of  it  with  that  modest  reserve 
which  characterizes  men  of  superior  excellence.  They 
propose  the  word  in  order  to  avoid  circumlocutions 
and  to  render  the  language  of  science  more  concise, 
rather  than  to  introduce  a  new  opinion. 

One  of  these  philosophers,  whom  science  and  man- 
kind still  mourn,  thus  expresses  himself  in  his  ad- 
mirable Traite  Rlcmentaire  de  Chimie :  "In  the  labours 
which  M.  de  Morveau,  M.  Berthollet,  M.  de  Fourcroy, 
and  myself  have  performed  in  common  on  the  reform 
of  the  language  of  chemistry,  we  have  felt  that  we  ought 
to  banish  from  it  those  circumlocutions  which  render 
the  form  of  expression  longer  and  more  cumbersome, 
less  exact,  and  less  clear,  and  which  not  seldom  even  do 
not  allow  of  ideas  sufficiently  well  defined.  We  have, 
therefore,  designated  the  cause  of  heat,  the  eminently 
elastic  fluid  which  produces  it,  by  the  name  caloric.  In- 
dependently of  the  fact  that  this  expression  answers  our 
purpose  in  the  system  which  we  have  adopted,  it  has 
besides  another  advantage,  that  of  being  able  to  adapt 
itself  to  all  sorts  of  opinions,  since,  strictly  speaking, 
we  are  not  even  obliged  to  suppose  that  caloric  is  a 
material  substance." 

If  the  point  in  question,  the  existence  or  non-exist- 
ence of  caloric,  were  less  important  we  might  be  content 
with  leaving  it  undecided  ;  but  the  use  of  heat  is  so 
general,  and  the  art  of  exciting  and  directing  it  is  so 
intimately  connected  with  the  perfecting  of  all  the  me- 
chanical arts  and  with  a  great  number  of  domestic  ap- 
plications, that  we  cannot  take  too  much  trouble  in 
becoming  acquainted  with  it. 

Without  entering  into  the  details  of  the  various  ex- 


Reflections  on  Heat.  169 

periments  which  have  been  performed  in  order  to  de- 
termine the  nature  of  heat,  I  will  limit  myself  in  this 
memoir  to  some  of  the  principal  results  of  these  re- 
searches. 

A  very  remarkable  phenomenon,  and  one  which  must 
have  been  noticed  as  soon  as  men  had  any  acquaintance 
with  fire,  is  the  radiation  from  solid  bodies  as  soon  as 
they  become  very  warm. 

When  a  solid  body  —  a  bar  of  iron,  for  example  —  is 
at  about  the  temperature  of  the  surrounding  air,  we 
do  not  see  or  perceive  anything  which  indicates  that  it 
possesses  a  radiating  surface ;  but  if  we  heat  it  strongly 
in  the  glowing  fire  of  a  forge,  the  body  changes  color, 
becomes  at  first  red,  then  white,  is  visible  in  the  dark, 
lights  up  surrounding  objects,  and  warms  in  a  sensible 
degree  all  objects  which  are  struck  by  the  rays  which 
it  emits  in  all  directions. 

If  we  allow  it  to  cool  slowly  in  the  undisturbed  air 
of  a  dark  room,  we  see  that  it  changes  color  again  ;  from 
white  it  becomes  red,  then  a  darker  red;  the  light  which 
it  gives  forth  gradually  diminishes  ;  the  intensity  of  its 
calorific  rays  becomes  less  at  the  same  time,  and  soon 
it  ceases  to  shed  light  round  about  it. 

It  continues,  however,  to  emit  from  its  surface  calo- 
rific rays  for  some  time  after  it  has  ceased  to  be  lumi- 
nous, as  may  be  perceived  by  holding  the  hand  near  it. 

The  calorific  rays  which  very  warm  bodies  send  off 
from  their  surfaces  pass  through  the  transparent  air 
without  heating  it,  nor  do  they  heat  sensibly  those 
bodies  at  whose  surfaces  they  are  reflected. 

These  very  important  facts,  which  ought  not  to  be 
forgotten,  have  been  established  by  the  results  of  a 
large  number  of  experiments. 


170  Reflections  on  Heat. 

We  have  thus  taken  one  sure  step  in  the  investigation 
of  heat.  We  see  that  very  warm  bodies  emit  from 
their  surfaces  rays  which,  passing  (like  rays  of  light) 
through  the  air  excite,  at  a  distance,  heat  at  the  surfaces 
of  the  surrounding  objects  on  which  they  fall  without 
being  reflected. 

The  existence  of  the  calorific  rays,  which  we  are  now 
discussing,  being  actually  proved,  and  their  manner  of 
acting  being  evidently  as  I  have  described  it,  it  is  im- 
portant to  ascertain  whether  the  knowledge  of  these  facts 
be  not  sufficient  to  form  a  theory  of  heat  which  will  ex- 
plain all  these  phenomena. 

A  theory  which  should  have  the  advantage  of  ex- 
plaining the  communication  of  heat  by  a  single  method, 
at  once  simple  and  easily  understood,  would  be  prefera- 
ble, it  seems  to  me,  to  one  which,  in  order  to  explain 
various  phenomena,  would  be  obliged  to  admit  two 
different  modes  of  the  communication  of  heat. 

In  order  to  form  a  clear  and  exact  idea  of  the  rays  in 
question  and  of  the  effects  which  they  are  capable  of 
producing,  we  must  go  back  to  their  mechanical  cause, 
and  consider  them  with  regard  both  to  their  existence 
and  to  their  operation. 

There  are  two  ways  of  looking  at  the  radiation  from 
an  object ;  the  first,  by  conceiving  the  rays  as  emana- 
tions of  an  actual  substance  thrown  off  from  the  surface 
of  the  body ;  the  second,  by  considering  these  rays  as 
undulations  which,  starting  from  every  point  of  the  sur- 
face of  the  radiating  object,  are  propagated  in  all  direc- 
tions in  straight  lines  in  an  elastic  fluid  which  surrounds 
it  on  every  side. 

The  system  of  Newton  supposes  that  the  rays  of  light 
are  real  emanations. 


Reflections  on  Heat.  171 

Sound,  with  which  we  are  better  acquainted  than  we 
are  with  light,  affords  us  an  example  of  radiation  or 
undulation  in  an  elastic  fluid  which  most  certainly  is 
not  an  emanation. 

We  have  sufficiently  clear  ideas  of  the  mechanical 
operations  by  means  of  which  the  undulations  of  the 
air  which  constitute  sound  are  excited  and  propagated ; 
but  We  have  no  conception  of  any  possible  mechanical 
operation  by  means  of  which  a  material  substance  could 
be  sent  forth  continually  and  in  all  directions  from  the 
surface  of  a  body. 

In  physics,  in  order  that  an  hypothesis  may  be  ad- 
mitted, it  must  be  founded  on  the  supposition  of  a  con- 
ceivable mechanical  operation. 

In  order  that  the  theory  of  heat  which  is  founded  on 
the  vibratory  hypothesis  may  be  admitted,  it  is  neces- 
sary to  show  that  the  vibrations  in  question  can  exist, 
and  that  they  can  cause  the  rays  or  undulations  which 
objects  emit  from  their  surfaces,  and  by  means  of  which 
we  suppose  that  bodies  of  different  temperatures  influ- 
ence each  other  even  at  a  distance,  bringing  about 
reciprocal  and  simultaneous  changes  of  temperature,  so 
that  little  by  little  they  arrive  at  a  common  and  inter- 
mediate temperature. 

If  the  particles  which  compose  a  body  do  not  touch 
each  other  (an  opinion  which  is  generally  received,  and 
which  appears  very  probable),  as  there  is  no  doubt  that 
these  particles  are  continually  drawn  one  towards  an- 
other by  the  recognized  force  of  universal  gravitation, 
it  is  impossible  to  conceive  how,  in  an  assemblage  of 
particles  which  form  a  tangible  solid  body,  these  parti- 
cles can  preserve  their  relative  situations  without  being 
in  motion. 


172  Reflections  on  Heat. 

From  this  course  of  reasoning  we  might  conclude 
that  the  particles  which  compose  a  body  are  of  necessity 
in  motion ;  and  if  we  admit  the  existence  of  an  emi- 
nently elastic  fluid,  —  an  ether  which  fills  all  space 
throughout  the  universe,  with  the  exception  of  that 
occupied  by  the  scattered  particles  of  ponderable  bodies, 
—  it  is  easy  to  conceive  that  the  movements  of  the 
particles  which  make  up  material  objects  must  cause 
undulations  in  this  fluid  ;  and,  on  the  other  hand,  the 
undulations  of  this  fluid  must  affect  to  a  sensible  de- 
gree and  modify  the  motions  of  the  particles  of  these 
bodies. 

It  might  perhaps  seem  that  these  motions  among  the 
particles  of  solid  bodies  would  be  incompatible  with  the 
preservation  of  the  forms  of  those  bodies ;  but  by  re- 
flecting attentively  on  this  subject  it  will  be  found  that 
such  motions  as  are  here  supposed  can  well  exist  with- 
out diminishing  at  all  the  stability  of  the  external  form 
of  the  bodies. 

It  would  follow  necessarily,  from  the  state  of  things 
supposed  by  the  hypothesis  in  question,  first,  that  the 
sum  of  the  active  forces  in  the  universe  must  always 
remain  constant,  in  spite  of  all  actions  and  reactions 
taking  place  among  the  various  bodies ;  secondly,  that 
the  particles  of  all  ponderable  bodies  must  of  necessity 
have  the  property  of  producing  radiations. 

Now,  if  we  admit  the  existence  of  the  ether,  it  is  pos- 
sible to  explain  the  radiations  of  bodies  in  still  an- 
other manner ;  it  is  by  supposing  that  the  particles 
are  kept  apart  from  each  other,  not  in  consequence  of 
the  action  of  the  centrifugal  force  of  those  particles,  but 
by  atmospheres  composed  of  ether  or  of  some  other 
fluid  unknown  to  us,  which  is  extremely  elastic,  and 


Reflections  on  Heat.  173 

that  it  is  by  the  very  rapid  vibrations  which  take  place 
in  these  atmospheres  that  those  undulations  in  the  sur- 
rounding ether  are  excited  by  means  of  which  the  tem- 
perature of  objects  is  altered. 

The  adoption  of  this  latter  hypothesis  will  reconcile, 
to  a  certain  extent,  the  theory  of  vibrations  with  that 
of  a  calorific  substance;  but  still  the  heating  of  a  body 
cannot  be  regarded,  in  any  respect,  as  the  result  of  the 
accumulation  of  this  substance,  but  as  the  acceleration 
of  its  motion. 

In  order  to  establish  on  a  firm  foundation  the  theory 
of  heat  which  is  based  upon  the  vibratory  hypothesis, 
it  is  necessary  not  only  to  show  that  the  vibrations  in 
question  are  possible,  but  also  to  prove  that  the  undu- 
lations which  they  should  cause  do  really  exist. 

In  the  ordinary  condition  of  things,  the  objects  which 
surround  us  do  not  afford  any  indication  of  radiation, 
nor  do  they  produce  any  effect  capable  of  manifesting 
itself  to  any  one  of  our  senses  in  such  a  way  as  to  lead 
us  to  suspect  that  they  possess  radiating  surfaces.  But 
the  philosopher  who  aims  at  penetrating  into  the  mys- 
teries of  Nature  must  be  continually  on  his  guard  that 
he  may  not  be  deceived  either  by  the  testimony  or  by 
the  silence  of  his  senses. 

In  the  first  place  it  is  evident  that  our  various  organs 
were  formed  with  reference  to  the  daily  wants  of  life ; 
and  that,  if  they  were  too  sensitive,  the  pleasure  which 
they  afford  us  would  be  turned  into  actual  pain. 

If  our  ears  had  been  constructed  so  as  to  be  sensibly 
affected  by  all  the  vibrations  which  take  place  in  the 
air,  we  should,  without  doubt,  be  stunned  by  the 
intolerable  noise,  even  in  the  deepest  retirement ;  and 
if  our  eyes  took  cognizance  of  all  the  rays  that  strike 


174  Reflections  on  Heat. 

them,  we  should  be  dazzled  by  an  insupportable  flood 
of  light,  even  in  the  darkest  night. 

It  is  well  known  that,  if  the  vibrations  of  a  sonorous 
body  be  less  frequent  than  30  in  a  second,  or  more 
frequent  than  3000  in  a  second,  the  undulations  of 
the  air  caused  by  these  vibrations  do  not  perceptibly 
affect  our  organs  of  hearing ;  and  it  is  very  probable 
that  the  range  of  our  organs  of  sight  is  still  more 
limited. 

When  we  have  found  strong  reasons  for  suspecting 
the  existence  of  agents  which  fail  to  manifest  themselves 
to  our  senses,  we  ought  to  employ  all  our  skill  in  devis- 
ing means  for  compelling  them  to  discover  themselves 
and  to  unveil  the  mysteries  of  their  invisible  operations. 

By  means  of  an  instrument  which  I  have  called  a 
thermoscope,  and  which  is  extraordinarily  sensitive,  I  have 
found  not  only  that  all  bodies  at  all  temperatures  emit 
rays,  but  also  that  the  rays  emanating  from  cold  bodies 
are  as  effectual  in  cooling  warm  bodies  as  the  rays  from 
the  latter  are  effectual  in  warming  cold  bodies. 

The  principal  part  of  the  instrument  of  which  I  have 
made  use  in  these  delicate  experiments  consists  of  a 
long  glass  tube  bent  at  both  ends,  and  having  at  each 
extremity  a  very  thin  glass  bulb  an  inch  and  a  half  in 
diameter.  The  middle  portion  of  this  tube,  which  is 
straight,  is  placed  in  a  horizontal  position,  while  the  two 
end  portions,  whose  extremities  are  the  two  bulbs,  are 
turned  upwards  in  such  a  way  as  to  form  right  angles 
with  the  horizontal  portion  of  the  tube.  The  hori- 
zontal portion  is  from  15  to  16  inches  in  length,  and 
each  of  the  two  end  portions,  which  are  vertical,  is 
from  6  to  7  inches  long.  The  internal  diameter  of 
the  tube  should  be  about  half  a  line. 


Reflections  on  Heat.  175 

By  means  of  a  little  glass  reservoir,  an  inch  in  length 
and  a  line  in  internal  diameter,  inserted  in  the  tube  at 
one  of  the  elbows,  there  is  introduced  into  the  interior 
of  the  instrument  a  small  quantity  of  coloured  spirit 
of  wine  (exactly  enough  to  fill  the  reservoir  without 
interfering  with  the  free  passage  of  the  air  from  one 
bulb  to  the  other) ;  this  being  done,  the  extremity  of 
the  reservoir  is  sealed  hermetically,  and  all  communica- 
tion between  the  air  enclosed  in  the  instrument  and  the 
air  of  the  outside  atmosphere  is  forever  interrupted. 

The  instrument  is  adjusted  and  prepared  for  use  as 
follows :  — 

The  bulb  which  is  farthest  from  the  reservoir  having 
been  warmed  slightly  with  the  hand,  the  instrument  is 
suddenly  turned  over,  so  as  to  bring  the  reservoir 
uppermost,  and  in  this  way  a  small  quantity  of  the 
spirit  of  wine  passes  from  the  reservoir  into  the  hori- 
zontal part  of  the  tube ;  restoring  immediately  the  in- 
strument to  its  natural  position,  the  observer  withdraws 
himself  from  it,  and  waits  for  the  small  quantity  of 
spirit  of  wine  which  has  passed  into  the  horizontal  part 
of  the  tube  to  become  stationary ;  this  will  be  as  soon 
as  the  two  bulbs  have  acquired  the  same  temperature. 

The  little  bubble  of  spirit  of  wine,  wh'ch  serves  as 
the  index  of  the  instrument,  and  which  may  be  about 
three  quarters  of  an  inch  long,  should  become  station- 
ary nearly  in  the  middle  of  the  horizontal  portion  of  the 
tube ;  if  it  is  too  near  either  of  the  elbows  it  must  be 
returned  to  the  reservoir,  and  the  operation  performed 
anew. 

When  this  delicate  operation  is  finished,  the  instru- 
ment is  ready  for  use.  The  method  of  employing  it  is 
as  follows  :  — 


I  ;5  Reflections  on  Heat. 

One  of  the  two  bulbs  is  protected  from  the  influence 
(calorific  or  frigorific)  of  the  warm  or  cold  bodies  pre- 
sented to  the  other  bulb  by  means  of  light  screens  cov- 
ered with  gilt  paper;  when  the  air  in  this  latter  bulb  is 
warmed  or  cooled  by  a  body  warmer  or  colder  than  the 
thermoscope  to  which  it  is  thus  presented,  the  elasticity 
of  the  air  is  affected  by  this  change  of  temperature,  and 
the  little  bubble  or  column  of  spirit  of  wine  which  is  in 
the  horizontal  portion  of  the  tube  is  compelled  to  move 
and  to  take  a  new  position. 

The  direction  of  the  motion  of  this  bubble  indicates 
the  nature  of  the  change  which  has  taken  place  in  the 
temperature  of  the  air  which  is  enclosed  in  the  bulb  to 
which  the  body  is  presented,  and  the  distance  traversed 
by  the  bubble  is  the  measure  of  the  increase  or  diminu- 
tion of  the  elasticity,  and,  as  a  consequence,  of  the  tem- 
perature of  that  air. 

If  the  bubble  recedes  from  the  bulb  to  which  the 
object  experimented  upon  is  presented,  it  is  evident 
that  the  air  enclosed  in  the  bulb  has  been  heated  by  the 
influence  of  this  body ;  but  when  the  bubble  of  spirit 
of  wine  advances  towards  this  bulb,  we  have  a  proof 
that  the  air  in  the  bulb  has  been  cooled. 

The  rapidity  with  which  the  bulb  moves  is  propor- 
tional to  the  intensity  of  the  action  of  the  object  pre- 
sented to  the  instrument. 

In  order  to  compare  the  intensity  of  the  calorific  or 
frigorific  actions  of  two  different  objects,  they  are  pre- 
sented at  the  same  time  to  the  two  bulbs  of  the  instru- 
ment, and  their  respective  distances  from  the  bulbs  so 
regulated  that  the  bubble  of  spirit  of  wine  remains  at 
rest  in  its  proper  position. 

In  this  case  it  is  evident  that  the  action  of  the  two 


Reflections  on  Heat.  177 

objects,  each  on  the  bulb  to  which  it  is  presented,  is  of 
precisely  the  same  amount;  hence  we  can  calculate  the 
relative  intensity  of  the  radiation  of  each  one  of  the 
two  objects  from  the  extent  of  the  surface  presented 
to  the  bulb,  and  from  the  square  of  its  distance  from 
the  bulb. 

If  we  desire  to  compare  the  calorific  action  of  a  warm 
body  with  the  frigorific  action  of  a  cold  body,  we  begin 
by  protecting  one  of  the  bulbs  of  the  instrument  by  the 
screens,  and  then  present  to  the  other  bulb  the  two 
objects,  —  regulating  their  respective  distances  in  such  a 
manner  that  their  actions  exerted  at  the  same  time  pro- 
duce equal  effects,  that  is,  so  that  one  warms  the  bulb 
as  much  as  the  other  cools  it. 

The  equality  in  the  amount  of  action  is  denoted  by 
the  remaining  at  rest  of  the  bubble  of  spirit  of  wine 
which  serves  as  the  index  of  the  instrument,  and  when 
this  equality  is  established,  the  relative  intensity  of  the 
radiation  from  the  objects  in  question  is  calculated  from 
the  amount  of  surface  which  they  respectively  present  to 
the  bulb,  and  from  the  squares  of  their  distances  from  it. 

The  sensibility  of  this  instrument  is  so  great  that, 
when  it  is  at  a  temperature  of  15°  or  16°  of  Reaumur's 
scale,  if  the  hand  be  presented  to  one  of  the  bulbs  at  a 
distance  of  three  feet,  the  heat  radiating  from  the  hand 
is  sufficient  to  cause  the  bubble  of  spirit  of  wine  to  move 
forward  several  lines;  and.  the  cooling  influence  of  a 
blackened  metallic  disk  four  inches  in  diameter,  at  the 
temperature  of  melting  ice,  is  such  that,  when  presented 
to  the  bulb  at  a  distance  of  18  inches,  it  causes  the  bub- 
ble to  advance  in  the  opposite  direction  with  a  rapidity 
which  is  very  perceptible  to  the  eye. 

By    means    of  this    instrument    I    have    discovered, 


178  Reflections  on  Heat. 

first,  that  all  bodies  at  all  temperatures  (cold  bodies  as 
well  as  warm  ones)  emit  continually  from  their  surfaces 
rays,  or  rather,  as  I  believe,  undulations^  similar  to  the 
undulations  which  sonorous  bodies  send  out  into  the 
air  in  all  directions,  and  that  these  rays  or  undulations 
influence  and  change,  little  by  little,  the  temperature  of 
all  bodies  upon  which  they  fall  without  being  reflected, 
in  case  the  bodies  upon  which  they  fall  are  either  warmer 
or  colder  than  the  body  from  the  surface  of  which  the 
rays  or  undulations  proceed  ;  secondly,  that  the  inten- 
sity of  the  rays  from  different  bodies  at  the  same  tem- 
perature is  very  different,  and  that  it  is  less  in  bodies 
which  reflect  the  rays  of  light  than  in  those  which  ab- 
sorb them,  less  in  the  metals  than  in  their  oxides,  less 
in  opaque  and  polished  bodies  than  in  those  which  are 
imperfectly  transparent  and  unpolished,  (a  surface  of 
brass,  for  instance,  emits  four  times  as  large  a  quantity 
of  rays  at  a  given  temperature  when  it  is  covered  with 
a  coating  of  oxide,  and  five  times  as  large  a  quantity 
when  it  is  blackened  by  the  flame  of  a  candle,  as  when 
the  surface  of  the  metal  is  clean  and  well  polished) ; 
thirdly,  that  the  rays  which  bodies  of  the  same  tem- 
perature send  out  to  each  other  have  no  tendency  to 
bring  about  any  change  of  temperature  in  these  bodies ; 
fourthly,  that  the  rays  which  any  body  whatever,  at  a 
given  temperature,  sends  continually  from  its  surface  in 
all  directions,  are  calorific  or  frigorific  with  regard  to 
other  bodies  on  which  they  fall,  according  as  these  latter 
are  less  warm  or  warmer  than  the  body  from  which  the 
rays  come;  so  that  the  same  rays  are  calorific  as  re- 
gards all  bodies  less  warm  than  the  one  from  which 
they  proceed,  and  frigorific  as  regards  all  those  which 
are  warmer  than  this  body. 


Reflections  on  Heat.  179 

From  these  facts  we  might  conclude  a  priori,  that 
those  bodies  which,  when  warm,  give  off  many  calorific 
rays  would,  when  colder  than  the  surrounding  objects, 
give  off  to  them  many  frigorific  rays.  This  is  exactly 
what  my  experiments  have  made  evident  to  me. 

In  experiments  made  with  bodies  of  the  same  size, 
and  of  the  same  material,  the  intervals  of  temperature 
being  equal,  the  frigorific  influences  of  cold  bodies  have 
always  appeared  as  real  and  effective  as  the  calorific  in- 
fluences of  warm  bodies. 

To  one  of  the  bulbs  of  a  thermoscope,  the  tempera- 
ture of  which  was  20°  of  Reaumur's  thermometer,  were 
presented  at  the  same  time  and  at  equal  distances  two 
disks  of  metal  of  the  same  diameter.  The  temperature 
of  one  of  these  disks  was  o°  (that  of  melting  ice),  that 
of  the  other  was  40°.  The  index  of  the  instrument  by 
remaining  at  rest  showed  that  the  bulb  was  cooled  by 
the  rays  from  the  cold  body  as  much  as  it  was  heated 
by  the  rays  from  the  warm  body. 

If  the  surface  of  one  of  the  disks,  it  matters  not  of 
which,  is  blackened,  the  intensity  of  the  radiation  from 
this  blackened  disk  is  increased  to  such  an  extent  that 
the  other  can  no  longer  counterbalance  it;  but  if  the 
second  one  is  blackened  also,  the  equality  of  action  is 
immediately  re-established. 

If  the  emanations  from  warm  and  cold  bodies  are 
really  undulations  in  an  extremely  rare  and  elastic  fluid 
which  has  been  called  ether,  the  communication  of  heat 
and  cold  ought  to  be  similar  to  the  communication  of 
sound  ;  and  all  the  mechanical  contrivances  which  have 
been  invented  to  increase  the  intensity  of  sound  ought 
to  be  just  as  applicable  for  increasing  the  effects  pro- 
duced by  these  emanations  from  warm  and  cold  bodies ; 


180  Reflections  on  Heat. 

and,  indeed,  I  found  that  a  speaking-tube  (a  conical 
brass  tube,  well  polished  on  the  inside)  placed  between 
one  of  the  bulbs  of  the  thermoscope  and  a  hollow  ball 
of  thin  copper  3  inches  in  diameter,  which,  being  filled 
with  pounded  ice,  was  presented  to  it  at  a  distance  of 
12  inches,  increased  more  than  three  times  the  effect  of 
the  cold  body. 

To  use  a  rather  strong  metaphor,  but  one  which  ex- 
presses perfectly  the  idea  which  I  have  conceived  of  the 
mechanical  operation  in  question,  I  will  say  that  the 
cold  ball  spoke  at  the  larger  opening  of  the  speaking- 
tube  while  the  bulb  of  the  thermoscope  listened  at  the 
smaller  opening. 

If  it  is  true  that  the  particles  which  make  up  all 
material  bodies  are  agitated  continually  by  very  rapid 
vibratory  motions,  and  that,  in  consequence  of  these 
motions,  all  bodies  at  all  temperatures  send  continually 
from  every  point  of  their  surfaces  rays  or  undulations 
similar  to  the  undulations  caused  in  the  air  by  the 
vibration  of  sonorous  bodies;  and  if  bodies  of  different 
temperatures  act  one  upon  another  at  a  distance,  by 
means  of  these  rays  or  undulations,  working  simultane- 
ously an  interchange  in  temperature  and  gradually 
bringing  about  a  mean  intermediate  temperature,  —  we 
ought  then  to  regard  the  cooling  of  a  warm  body  as  the 
result  of  the  actual  and  positive  operation  of  the  sur- 
rounding bodies  less  warm  than  itself;  and  since  the 
rays  coming  from  warm  bodies,  and,  as  a  consequence, 
from  cold  bodies,  are  reflected  in  great  measure  by  the 
polished  surfaces  of  opaque  bodies,  and  since  the  rays 
which  are  reflected  produce  little  or  no  effect  on  the 
bodies  at  whose  surfaces  they  are  reflected,  we  might 
conclude  a  priori  that  opaque  polished  bodies  ought  to 


Reflections  on  Heat.  181 

cool  or  become  warm  more  slowly  than  bodies  imper- 
fectly transparent  and  unpolished. 

I  will  now  detail  the  results  of  a  series  of  experiments 
made  with  a  design  of  throwing  light  on  this  point,  so 
important  in  the  science  of  heat. 

I  had  made  two  cylindrical  vessels,  four  inches  in 
diameter  and  four  inches  high,  of  thin  sheet  brass,  well 
polished  on  the  outside.  Having  blackened  one  of 
them  over  the  flame  of  a  candle,  I  filled  them  both  with 
boiling  water,  and  left  them  at  the  same  time  to  cool  in 
the  air  of  a  large  quiet  room.  The  one  which  was  black- 
ened cooled  almost  twice  as  fast  as  the  one  whose  metal- 
lic surface  remained  bright  and  clean.  When  the  two 
vessels  had  become  of  the  same  temperature  as  that  of 
the  room  in  which  they  were  situated,  they  were  re- 
moved into  a  room  warmed  by  a  stove,  and  I  found 
that  the  blackened  vessel  was  heated  twice  as  quickly  as 
the  other. 

The  blackened  vessel  was  cleaned  and  covered  with  a 
single  covering  of  fine  linen,  fitting  closely  to  the 
body  of  the  instrument.  Repeating  the  experiments 
with  the  two  vessels,  that  which  was  exposed  naked  to 
the  cold  air  took  up  45  minutes  in  cooling  through  an 
interval  of  10  degrees  on  Fahrenheit's  scale,  that  is,  from 
the  5oth  to  the  4Oth  degree  above  the  temperature  of 
the  room ;  the  other  vessel,  covered  with  a  coat  of  fine 
linen,  took  up  only  29  minutes  in  cooling  through  the 
same  interval. 

When  the  two  vessels  had  become  of  the  same  tem- 
perature, they  were  removed  into  a  warm  room,  and  I 
found  that  the  vessel  which  was  clothed  with  linen 
acquired  heat  faster  than  the  one  whose  surface  was 
naked. 


1 82  Reflections  on  Heat. 

If  the  results  of  these  experiments  do  not  furnish  a 
conclusive  proof  of  the  radiation  from  all  bodies,  and 
that  it  is  by  means  of  these  radiations  from  surrounding 
objects  that  the  temperature  of  a  given  body  is  changed, 
they  certainly  lend  to  this  conjecture  a  great  degree  of 
probability. 

Several  other  similar  experiments  were  undertaken  in 
order  to  throw  light  on  this  point,  and  results  were  in- 
variably obtained  which  tended  to  confirm  the  hypothe- 
sis in  question. 

Of  all  known  bodies  the  metals  are  the  most  opaque, 
and  it  appears  that  they  are  so  to  an  equal  degree  ;  it 
appears  also  that  a  naked  metallic  surface,  or  one  that  is 
free  from  all  dirt,  is  always  polished  in  spite  of  those 
irregularities  of  form  by  which  the  brilliancy  of  its  metal- 
lic lustre  is  broken  up  and  apparently  diminished.  If 
these  conjectures  are  well  founded,  we  may  conclude  that 
all  metals  are  equally  competent  to  reflect  from  their 
surfaces  the  rays  that  impinge  upon  them ;  and  if  ob- 
jects are  heated  and  cooled  by  rays  from  surrounding 
objects,  we  might  conclude  not  only  that  of  all  known 
bodies  the  metals  ought  to  acquire  heat  or  become  cold 
the  least  rapidly,  but  also  that  they  ought  to  acquire 
heat  or  become  cold  with  the  same  degree  of  difficulty 
or  rapidity. 

To  put  these  suppositions  to  the  test  of  experiment, 
I  procured  several  cylindrical  vessels,  of  the  same  form 
and  dimensions  but  of  different  metals,  and  I  found 
that  they  did  indeed  all  cool  or  acquire  heat  in  the 
same  time.  There  were  vessels  of  brass,  tin,  lead,  and 
others  covered  with  thin  coatings  of  gold  and  silver; 
each  vessel  was  four  inches  in  diameter  and  four  inches 
high,  and  when  filled  with  boiling  water  and  exposed,  in 


Reflections  on  Heat.  183 

winter,  to  the  air  of  a  large  quiet  room,  they  all 
passed,  in  cooling,  through  the  given  interval  of  10  de- 
grees in  from  45  to  46  minutes. 

This  equality  in  the  degree  of  readiness  with  which 
all  the  metals  become  cool  or  acquire  heat  is  certainly 
very  remarkable  ;  and  it  seems  to  me  very  difficult  of 
explanation  except  by  adopting  the  hypothesis  that  heat 
is  communicated  by  means  of  radiations. 

As  it  might  be  supposed  that  a  film  of  air,  attached 
by  a  certain  force  of  attraction  to  the  surfaces  of  the 
metallic  vessels,  could  have  caused  this  apparent  equal- 
ity in  their  rate  of  cooling,  I  made  the  following  ex- 
periments to  elucidate  this  point. 

One  of  the  two  brass  vessels  was  covered,  first  with 
one,  next  with  two,  then  with  four,  and  finally  with 
eight  coatings  of  spirit  varnish,  and  the  experiment  with 
the  two  vessels  was  repeated  with  each  of  these  coatings. 
While  the  vessel,  the  surface  of  which  was  bare,  cooled 
invariably  through  the  given  interval  of  10  degrees  in 
45  minutes,  the  other  vessel,  which  was  varnished, 
cooled  more  or  less  rapidly  according  to  the  thickness 
of  the  coating  of  varnish  with  which  its  surface  was  cov- 
ered, but  always  in  a  sensible  degree  more  rapidly  than 
the  one  whose  surface  was  naked :  — 

Minutes. 

With  one  coating  of  varnish  it  cooled  in  .         .  34i 

With  two  coatings,  in 29 

With  four  coatings,  in 24^ 

And  with  eight  coatings,  in    .         .         .         .         .  27 

As  the  film  of  air  which  is  supposed  to  have  been 
attached  to  the  surface  of  the  vessel  when  this  metal- 
lic surface  was  not  covered  with  varnish  ought  to  have 
been  as  completely  driven  off  by  one  coating  of  varnish 


184  Reflections  on  Heat. 

as  by  two  or  by  a  greater  number,  it  seems  very  difficult 
to  reconcile  the  results  of  these  experiments  with  the 
supposition  that  a  film  of  air  attached  to  the  surfaces  of 
all  the  vessels,  made  as  they  were  of  different  metals, 
was  the  cause  of  their  cooling  all  equally  slowly. 

When  I  repeated  the  experiment  with  a  vessel  of  glass, 
and  with  one  of  tinned  iron  of  the  same  form  and  di- 
mensions, I  found  that  the  glass  vessel  cooled  much 
more  rapidly  in  the  air  than  the  one  made  of  tinned 
iron,  although  its  walls  were  six  times  as  thick  as  those 
of  the  latter.  In  water  the  vessel  of  tinned  iron  cooled 
most  rapidly. 

The  results  of  all  these  experiments,  and  of  a  great 
number  of  others  which  it  would  take  too  long  to  de- 
tail here,  convinced  me  that  the  ease  with  which  a  body 
is  heated  or  cooled  depends  very  much  on  the  nature 
of  the  surface  of  that  body,  —  these  operations  going  on 
more  slowly  and  with  more  difficulty  as  the  surface  of 
the  body  is  more  capable  of  reflecting  the  rays  which 
fall  upon  it;  I  was  therefore  impatient  to  submit  the 
theory  of  heat  which  I  had  adopted  to  the  most  search- 
ing of  tests,  by  employing  it  to  explain  some  of  the 
grand  and  interesting  phenomena  of  nature. 

Close  to  us  there  occurs  a  most  interesting  phenome- 
non, and  one  which,  assuredly,  is  calculated  to  excite 
our  curiosity. 

The  people  who  inhabit  hot  countries  are  black, 
while  those  who  dwell  in  cold  climates  are  white. 

What  advantages  do  the  negroes  derive  from  their 
colour  which  makes  them  better  fitted  than  the  whites 
for  supporting  without  inconvenience  the  excessive  heats 
of  their  scorching  climate  ? 

In  all  climates  a  large  amount  of  heat  is  necessarily 


Reflections  on  Heat.  185 

excited  in  the  lungs  by  the  act  of  breathing;  and  when 
man  is  placed  in  a  situation  where  the  air  and  all  objects 
about  him  are  almost  as  warm  as  his  blood,  the  sur- 
face of  his  body  ought  to  be  of  such  a  character  as  to 
be  readily  cooled  ;  else  the  rays,  very  slightly  cooling  in 
their  action,  which  reach  him  from  the  surrounding  ob- 
jects, would  not  suffice  to  free  him  from  the  heat  gener- 
ated continually  in  his  lungs,  and  he  would  soon  find 
himself  oppressed  and  overcome  by  the  accumulation  of 
this  heat. 

In  a  cold  country,  where  the  cooling  of  the  surface 
of  a  body  by  the  cold  objects  which  surround  it  is  more 
than  sufficient  to  counterbalance  the  heat  continually 
produced  by  respiration,  the  body  can  be  protected  from 
this  excessive  cooling  action  by  clothing ;  but  we  know 
of  no  sort  of  clothing  fitted  to  promote  sufficiently  the 
cooling  of  the  human  body  in  a  very  hot  climate. 

What  has  Nature  done  to  supply  this  want  ?  She 
has  given  to  the  inhabitants  of  hot  countries  a  black, 
skin ;  this  colour  gives  to  the  negro  such  facility  for 
becoming  cool  that  he  feels  perfectly  comfortable  in  a 
situation  where  a  white  man  would  be  overcome  by 
the  heat.  But,  in  return,  the  negro  shivers  with  cold 
in  a  climate  which  the  white  man  finds  perfectly  agree- 
able. 

Every  one  knows  that  a  black  surface  reflects  fewer 
rays  of  light  than  a  white  surface ;  and  the  results  of 
all  the  experiments  performed  by  myself  and  by  others 
seem  to  show  that  those  surfaces  which  are  of  such  a 
character  as  to  reflect  light  also  reflect  the  calorific  or 
frigorific  rays  which  all  bodies  send  continually  from 
their  surfaces ;  and  if  the  temperature  of  a  body  is 
changed  in  consequence  of  the  action  of  surrounding 


1 86  Reflections  on  Heat. 

bodies  through  these  radiations,  it  is  seen  clearly  why 
the  negro  suffers  less  from  the  heat  of  the  tropics,  and 
more  from  the  cold  of  the  polar  regions,  than  the  man 
with  a  white  skin. 

But  when  the  negro  is  exposed  to  the  action  of  calo- 
rific rays  —  to  those  of  the  sun,  for  instance  —  must  he 
not  be  heated  more  than  a  white  man  ?  It  would  be  so, 
without  doubt,  if  Nature  had  not  foreseen  the  danger 
and  provided  means  for  warding  off  the  evil. 

When  the  negro  is  exposed  to  the  rays  of  the  sun,  an 
oily  matter  appears  immediately  at  the  surface  of  his 
skin,  and  causes  it  to  shine ;  the  calorific  rays  which 
fall  upon  it  are  reflected  to  a  great  extent,  and  he  finds 
himself  but  little  heated. 

The  sun  sets,  or  the  negro  enters  his  hut ;  the  oil 
which  covers  the  surface  of  his  body  retires  under  his 
skin,  and  he  retains  all  the  advantages  which  his  colour 
affords  in  aiding  him  to  become  cool. 

If  a  coating  of  oil  on  the  skin  serves  to  protect  the 
body  from  the  too  violent  action  of  calorific  rays,  it 
ought  to  serve  also,  without  doubt,  to  protect  it  from 
the  too  violent  action  of  frigorific  rays  in  very  cold 
countries,  especially  in  winter,  when  the  sun  never  rises. 
And,  indeed,  do  not  the  Laplanders  besmear  themselves 
with  oil  ? 

But  in  the  case  of  a  question  of  so  great  interest,  I 
wished  to  omit  nothing  which  might  throw  light  upon  it. 

The  following  experiment  seemed  to  me  to  establish 
beyond  doubt  the  principal  facts. 

Having  covered  two  of  my  cylindrical  vessels  with 
an  animal  substance,  namely,  with  gold-beater's  skin,  I 
painted  one  of  them  black  with  Indian  ink,  leaving  the 
other  of  its  natural  white  color.  Having  filled  both  of 


Reflections  on  Heat.  187 

the  vessels  with  hot  water,  I  left  them,  at  the  same  time, 
to  cool  in  the  air  of  a  large  quiet  room. 

The  vessel  covered  with  a  black  skin  represented  a 
negro  ;  the  one  covered  with  a  white  skin  represented 
a  white  man. 

The  negro  cooled  considerably  more  rapidly  than  the 
white  man,  requiring  23^  minutes  to  cool  through  the 
usual  interval  of  10  degrees,  while  the  white  man  re- 
quired 28  minutes  to  cool  through  the  same  interval. 

This  interesting  experiment  was  made  at  Munich,  the 
26th  of  March,  1803.  The  results  of  these  experi- 
ments need  no  illustration ;  and  I  leave  to  physiolo- 
gists and  physicians  to  determine  what  advantages  may 
be  derived  from  them  in  taking  measures  for  the  pres- 
ervation of  the  health  of  white  men  who  are  called 
upon  to  dwell  in  hot  countries. 

[This  paper  is  translated  from  the  Moniteur  Universe!,  9  Messidor, 
An  12  (June  26,  1804).] 


HISTORICAL     REVIEW 


VARIOUS   EXPERIMENTS   OF    THE  AUTHOR   ON   THE 
SUBJECT   OF  HEAT. 

A  WRITER  who  directs  the  attention  of  the  pub- 
lic to  a  work  upon  a  subject  as  important  as  it  is 
difficult  of  investigation  must  assuredly  be  allowed  at 
the  very  outset  to  state  modestly  the  reasons  which 
entitle  him  to  a  hearing.  It  is  also  equally  true  that 
a  natural  philosopher  can  with  justice  lay  claim  to  the 
confidence  and  approbation  of  the  learned  only  so  far 
as  his  claims  are  based  upon  his  own  labours,  upon 
toilsome  and  accurate  observations,  as  well  as  upon 
experiments  planned  and  executed  with  all  possible 
care. 

To  engage  in  experiments  on  heat  was  always  one 
of  my  most  agreeable  employments.  This  subject  had 
already  begun  to  excite  my  attention  when,  in  my 
seventeenth  year,  I  read  Boerhave's  admirable  Treatise 
on  Fire.  Subsequently,  indeed,  I  was  often  prevented 
by  other  matters  from  devoting  my  attention  to  it,  but 
whenever  I  could  snatch  a  moment  I  returned  to  it 
anew,  and  always  with  increased  interest.  Even  now 
this  object  of  my  speculations  is  so  present  to  my  mind, 
however  busy  I  may  be  with  other  affairs,  that  every- 
thing taking  place  before  my  eyes,  having  the  slightest 
bearing  upon  it,  immediately  excites  my  curiosity  and 
attracts  my  attention. 


Historical  Review  of  Experiments  on  Heat.     189 

This  habit  of  many  years'  standing,  by  force  of  which 
I  seize  with  the  greatest  eagerness,  and  endeavour  to 
investigate,  each  and  every  phenomenon  related  even 
in  the  slightest  manner  to  heat  and  its  operations  which 
comes  to  my  knowledge,  has  suggested  to  me  almost  all 
the  experiments  that  I  have  performed  with  reference  to 
this  subject. 

In  the  year  1778  I  was  engaged  in  investigating  the 
force  of  gunpowder  and  the  velocity  of  bullets  dis- 
charged from  fire-arms.  For  this  purpose  I  discharged 
many  times  a  musket-barrel  which  was  loaded  in  vari- 
ous ways,  and  which  rested  on  two  iron  rods,  perfectly 
free  (that  is,  without  any  stock),  in  a  horizontal  posi- 
tion, about  four  feet  from  the  ground.*  This  gave  me 
occasion  to  make  a  very  striking  observation. 

Since  these  experiments  were  intended  principally 
to  determine,  from  the  recoil  of  the  barrel,  the  veloci- 
ties with  which  the  bullets  were  discharged,  it  was 
first  necessary  to  ascertain  how  much  the  weight  of 
the  powder  which  caused  the  discharge  of  the  bullets 
had  to  do  with  this  recoil.  In  order  to  solve  this 
problem,  I  made  several  successive  experiments,  — 
some  with  a  charge  of  powder  without  any  bullet, 
and  some  with  two,  three,  or  even  four  bullets,  one 
upon  another. 

According  to  my  usual  practice,  I  seized  the  piece 
with  my  left  hand  immediately  after  each  discharge,  in 
order  to  hold  it  firmly  until  I  had  wiped  it  out  with 
some  tow  fastened  to  the  rammer.  I  was  therefore 
not  a  little  astonished  to  notice,  on  this  occasion,  that 

*  A  detailed  description  of  these  investigations  may  be  found  in  the  seventy-first 
volume  of  the  Philosophical  Transactions,  and  in  the  first  volume  of  my  Philosophical 
Papers,  which  was  published  at  London,  in  the  year  1802,  by  Cadell  and  Davics.  Sec 
also  Vol.  I.  p.  I.  ' 


igo  Historical  Review  of  Experiments 

the  barrel  was  always  hotter  when  the  charge  had  con- 
sisted of  powder  alone  than  when  loaded  with  one  or 
more  "bullets. 

I  had,  up  to  this  time,  no  suspicion  but  that  the 
piece,  on  being  discharged,  became  warm  as  an  immedi- 
ate consequence  of  the  heat  caused  by  the  burning  of 
the  gunpowder ;  now,  however,  I  was  convinced  by 
the  result  of  the  above-mentioned  experiment,  that  this 
supposition  was  entirely  without  foundation. 

For  if  we  should  hold  that  the  gun  in  question  was 
actually  heated  by  the  inflammation  of  the  powder, 
since  the  flame  would  issue  from  the  piece  much  more 
rapidly  when  the  charge  consisted  of  powder  alone  than 
when  the  same  charge  had  to  force  out  one  or  more 
bullets,  it  would  follow  that  a  much  higher  degree  of 
temperature  would  be  reached  in  the  latter  case  than  in 
the  former.  But  since  the  above-mentioned  experiment 
shows  the  contrary,  it  follows  that  the  heating  of  the 
piece  in  question  is  not  due  to  the  combustion  of  the 
powder,  but  to  the  vibrations  caused  by  the  concussion 
within  the  barrel,  and  to  the  operation,  as  rapid  as  it 
is  brief,  of  the  elastic  fluid  generated  by  this  com- 
bustion. 

No  one  is  ignorant  of  the  fact  that  a  heavy  blow  is 
much  more  effective  in  producing  heat  in  a  solid  body 
than  a  lighter  one  ;  and  if  the  hypothesis  be  well 
founded  that  heat  is  nothing  more  than  a  continu- 
ous, more  or  less  rapid,  vibratory  motion  among  the 
particles  of  solid  bodies,  this  phenomenon  is  easily 
explained. 

Nothing  is  more  certain  than  that  the  shock  taking 
place  within  the  barrel,  in  the  case  of  the  above-men- 
tioned experiment,  by  the  combustion  of  the  powder, 


on  the  Subject  of  Heat.  191 

was  more  vibrating  or  heavier  when  the  charge  was 
fired  without  a  bullet  than  when  the  elastic  fluid  gener- 
ated by  the  combustion  was  obliged,  in  order  to  get 
room  for  action,  to  push  slowly  before  it  one  or  more 
balls,  which  were  anything  but  light.  On  careful  con- 
sideration it  seems  to  me  that  this  circumstance  is  more 
than  sufficient  to  explain  in  a  satisfactory  manner  the 
results  of  the  experiments  in  question,  although  I  am 
perfectly  free  to  confess  that  I  never  could  reconcile 
myself  to  the  hypothesis  which  has  been  developed 
with  regard  to  caloric. 

The  above-mentioned  occurrence  made  so  deep  an  im- 
pression upon  me,  that  I  could  hardly  wait  long  enough 
to  procure  the  necessary  instruments  before  undertak- 
ing a  number  of  successive  experiments  upon  heat,  in 
order  to  arrive  at  some  conclusion  with  regard  to  its 
character,  as  well  as  to  the  manner  of  its  operation. 

I  proposed,  first  of  all,  to  undertake  various  experi- 
ments on  what  has  since  been  called  the  specific  heat  of 
bodies.  For  this  purpose,  I  procured  from  Mr.  Fra- 
ser,  New  Bond  Street,  London  (now  physical  and 
mathematical  instrument  maker  to  the  King  of  Eng- 
land), a  considerable  number  of  solid  balls  of  precisely 
the  same  diameter,  namely,  one  inch.  Some  of  these 
balls  were  of  gold,  some  of  silver  ;  in  short,  they  all  were 
of  one  metal  or  another,  or  of  some  solid  substance 
easily  turned  in  a  lathe.  Each  of  these  balls  was  sus- 
pended by  a  thin  silken  cord,  and  I  proposed  to  heat 
the  balls  in  certain  liquids  up  to  a  given  temperature, 
and  then  to  plunge  them  into  a  known  quantity  of  water 
which  had  been  cooled  in  the  same  proportion.  I  drew 
this  inference,  —  that  the  degree  of  temperature  which 
the  balls  communicated  to  the  known  amount  of  water, 


1 92  Historical  Review  of  Experiments 

as  shown  by  the  thermometer,  would  be  more  than  suf- 
ficient to  calculate  therefrom  the  proportional  amount 
of  heat  necessary  to  bring  to  the  same  temperature  the 
balls  and  an  equal  quantity  of  water. 

I  had  already  begun  upon  these  experiments,  but 
before  I  could  finish  them  the  war  made  it  necessary  for 
me  to  go  to  America.  These  researches  were  therefore 
interrupted  for  several  years  ;  and  when,  after  the  peace 
of  1783,  I  returned  to  England,  I  learned  that  Wilkin, 
in  Sweden,  had  already  carried  out  exactly  what  I  had 
proposed  to  myself.  Since  I  had  not  the  slightest 
occasion  to  doubt  the  accuracy  of  the  experiments 
performed  by  this  philosopher,  I  laid  aside,  as  useless, 
the  apparatus  which  I  had  designed  for  my  own  in- 
vestigations. 

In  the  following  year  I  left  England  and  went  to 
Bavaria,  where  I  was  received  into  the  service  of  the 
late  Elector.  I  brought  with  me  several  instruments 
belonging  to  the  above-mentioned  apparatus,  which  are 
still  to  be  seen  in  the  museum  of  the  military  school  in 
Munich. 

For  more  than  twenty  years  I  have  never  in  any  of 
my  writings  mentioned  either  my  project  and  the  prepa- 
rations made  for  carrying  out  experiments  on  this  point, 
or  the  experiments  I  really  made  and  which  agree  with 
those  of  Wilkin,  simply  because  I  hate,  and  always 
have  hated,  the  character  of  a  man  who  appropriates 
the  discoveries  of  another.  I  speak  of  them  now  rather 
to  convince  the  public  that  I  have  long  thought  about 
this  subject,  than  from  any  motive  which  might  perhaps 
have  its  origin  in  personal  vanity. 

My  relations  at  the  court  at  Munich,  and  that,  too, 
with  a  prince  who  was  much  interested  in  the  promo- 


on  the  Subject  of  Heat  193 

tion  of  knowledge,  afforded  me  during  a  period  of  four 
years  abundance  of  leisure  to  pursue,  almost  without 
interruption,  my  physical  investigations,  and  I  em- 
ployed this  leisure  in  making  a  considerable  number  of 
experiments  on  heat. 

In  the  years  1785  and  1786  I  was  occupied  in  re- 
searches as  to  the  manner  in  which  heat  passes  through 
various  substances  an4  communicates  itself  still  farther. 
A  detailed  description  of  these  experiments  is  to  be 
found  in  the  two  papers  which  I  inserted  in  the  Philo- 
sophical Transactions  of  the  Royal  Society  of  London. 
The  first  is  in  the  seventy-sixth,  the  other  in  the  eighty- 
third,  volume  of  this  work.  For  the  latter  I  received 
the  gold  medal  which  this  Society  is  accustomed  to  con- 
fer annually.* 

In  the  summer  of  1785  I  discovered  that  heat  could 
be  transmitted  through,  or  excited  in,  a  Torricellian 
vacuum. 

Since  this  discovery  has  contributed  not  a  little 
towards  strengthening  me  in  the  opinion  which  I  have 
since  adopted  with  regard  to  the  real  character  of  heat, 
I  do  not  consider  it  at  all  superfluous  to  give  here,  with 
all  its  details,  an  account  of  the  experiment  by  which 
this  fact  was  established  beyond  doubt.  This  experi- 
ment was  conducted  as  follows. 

After  a  skilful  workman  in  Mannheim,  Artaria  by 
name,  had  succeeded  in  fixing  firmly  the  globular  bulb 
of  a  mercurial  thermometer,  half  an  inch  in  diameter,  in 
the  centre  of  another  glass  bulb  an  inch  and  a  half  in 
diameter,  the  space  between  the  outer  surface  of  the 
thermometer  bulb  and  the  inner  surface  of  the  outside 
ball,  or  the  globe,  was  filled  with  mercury  by  means  of  a 

*  These  papers  were  printed  in  1797,  in  my  eighth  Essay.     Sec  Vol.  I.  p.  401. 
VOL.    II.  13 


194  Historical  Review  of  Experiments 

barometer  tube  which  was  soldered  to  a  small  hollow 
tube  or  point  projecting  outwards  from  the  globe.  This 
projection  extended  downwards  when  the  thermometer 
fastened  to  the  globe  was  in  its  natural  upright  posi- 
tion. 

As  soon  as  the  vacant  space  inside  of  the  globe  and 
around  the  thermometer  bulb,  as  well  as  the  barometer 
tube  (thirty-six  inches  in  length),  was  filled  with  mercury, 
the  end  of  the  tube  was  dipped  into  a  vessel  of  mer- 
cury ;  the  tube  was  then  inverted  and  brought  into  a 
perpendicular  position,  so  that  the  globe  in  which  the 
thermometer  was  fastened  was  at  the  top. 

Since  the  instrument  was  converted  in  this  way  into 
a  true  barometer,  the  mercury  in  the  globe  and  in 
the  upper  part  of  the  barometer  tube  fell  until  the 
upper  surface  of  the  mercury  in  the  tube  was  twenty- 
eight  inches  above  the  surface  of  the  mercury  in  the 
vessel,  where  it  remained  at  rest,  being  kept  at  this 
height  by  the  pressure  of  the  outside  air.  A  lighted 
wax-candle  was  now  held  at  the  upper  part  of  the 
tube  where  it  entered  the  globe,  and  where  the  diame- 
ter of  the  tube  had  previously  been  contracted,  and 
the  flame  was  directed,  by  means  of  a  blow-pipe,  against 
that  part  of  the  tube  which  it  was  desired  to  melt 
together. 

As  the  glass  was  softened  by  the  heat,  the  pressure 
of  the  outside  air  immediately  forced  the  walls  of  the 
tube  together ;  the  whole  operation  was  successful. 

The  barometer  tube  was  then  detached,  and  the  bulb 
of  the  thermometer  was  now  surrounded  on  all  sides  by 
a  vacuum,  as  may  be  seen  from  the  figure  on  the  oppo- 
site page.*  The  thermometer  was  filled  with  mercury, 

*  See  also  Vol.  I.,  Plate  to  p.  404,  Fig.  i. 


on  the  Subject  of  Heat. 


'95 


and  provided  with  a  scale,  and  I  could  then  scarcely 
master  my  impatience  and  wait  for  the.  time  when  I 
should  satisfy  myself  whether  heat  would  be  able  to 
pass  through  this  vacuum. 

I  now  put  the  apparatus  into  a  vessel  filled  with 
water  at  18°  Reaumur,  and  left  it  there  until  I  was  sure 
(from  the  scale  of  the  instrument)  that  the  bulb  filled 
with  mercury,  which  was  in  the  centre  of  the  vacuum, 
had  reached  this  temperature  of  18  degrees.  I  then 
took  the  instrument  out  of  this  vessel,  and  held  it  for 
some  minutes  in  another  full  of  hot  water,  which  was 
kept  constantly  boiling  by  a  lamp  placed  under  it. 

Since  the  mercury  in  the  tube  of  the  thermometer 
began  to  rise,  although  slowly,  there  remained  no  longer 
any  doubt  that  the  heat  of  the  boiling  water  really  passed 
through  the  vacuum  into  the  bulb  of  the  thermometer. 


196  Historical  Review  of  Experiments 

The  mercury  in  the  thermometer  rose  in  the  follow- 
ing manner :  After  the  instrument  had  remained  in  the 
boiling  water  i  min.  30  sec.  the  mercury  had  risen  from 
1 8°  to  27°.  After  the  lapse  of  4  minutes,  it  had  risen 
to  44T9o°:>  and  at  the  end  of  5  minutes  to  48  J°. 

In  order  to  estimate  more  accurately  the  relative 
rapidity  with  which  heat  passed  through  a  vacuum  and 
through  air,  I  broke  off  the  end  of  the  small  pointed 
tube  which  projected  from  the  under  side  of  the  globe 
so  that  the  air  could  freely  enter  the  globe ;  I  then 
melted  the  tube  together  a  second  time,  by  means  of  a 
candle ;  cooled  my  apparatus  in  water,  and  plunged  it, 
as  soon  as  it  had  acquired  the  temperature  of  this  water, 
that  is  1 8°,  again  into  boiling  water.  The  mercury  rose 
much  more  rapidly  than  in  the  preceding  experiment. 

The  manner  in  which  the  temperature  gradually  in- 
creased in  both  experiments  is  shown  in  the  following 
table. 

When  the  spherical  reservoir  of  the  mercurial  ther- 
mometer, which  was  fastened  in  the  centre  of  a  glass 
globe  an  inch  and  a  half  in  diameter,  was  plunged  into 
boiling  water,  the  times  of  ascent  were  as  follows  :  — 

In  a  Torricellian  vacuum.  Surrounded  by  air. 

(Exp.  No.  i.)  (Exp.  No.  2.) 

Time  Heat  Time  Heat 

elapsed.        acquired.  elapsed.         acquired. 

Upon  being  plunged  into  ~>  fi0  Q0 

boiling  water  } 

m.    s.  o  m.    s.  o 

After  remaining  in  it  I   30         27  o  45          27 

4  o         44-fr  2  10        44^ 

5  6         48J-  50         6oT% 

From  the  results  of  these  experiments  it  is  evident 
that  the  heat  increases  nearly  twice  as  fast  when  the  bulb 
is  surrounded  by  air  as  when  it  is  in  a  vacuum. 

I  afterwards  performed  other  experiments  of  the  same 


on  the  Subject  of  Heat.  197 

kind  without  discovering  the  least  difference  from  those 
mentioned  above.  It  would  take  too  much  time  and 
space  to  describe  them  all  here.  They  are  to  be  found, 
however,  in  my  memoir  in  the  Philosophical  Transac- 
tions and  in  my  eighth  Essay. 

I  had  subsequently  several  instruments  of  the  same 
sort  made,  in  order  to  repeat  and  vary  my  experiments. 
Sometimes  I  observed  the  time  which  they  took  in  cool- 
ing, sometimes  that  necessary  for  the  heat  to  penetrate 
them.  Sometimes  I  performed  the  experiment  in  the 
open  air,  sometimes  in  water.  All  these  experiments 
gave  the  same  result,  namely,  that  the  thermometer 
•  bulb  in  a  vacuum  became  warm  or  cold  as  the  case 
might  be,  the  only  difference  being  that  it  always  took 
nearly  twice  as  long  to  effect  this  change  of  temperature 
as  was  required  when  the  bulb  was  surrounded  by  air. 

The  passage  of  heat  through  a  vacuum  was  a  fact  of 
such  importance  in  the  investigation  of  the  nature  of 
heat,  that  I  wished  to  confirm  it  by  experiments  which 
would  not  allow  a  shadow  of  doubt. 

That  part  of  the  thermometer  tube  which  was  in- 
serted in  the  glass  globe  was  in  contact  with  this  globe. 
Hence  the  thought  might  suggest  itself  that  a  part  of 
the  heat  received  or  given  out  by  the  thermometer  bulb, 
which  was  surrounded  by  the  vacuum,  was.  communi- 
cated by  means  of  the  tube  of  the  thermometer,  since 
a  portion  of  this  tube  was  surrounded  by  air  or  water  in 
which  the  heating  or  cooling  was  effected.  In  order  to 
be  fully  satisfied  as  far  as  this  circumstance  was  con- 
cerned, it  occurred  to  me  to  repeat  the  experiment  with 
a  thermometer  suspended  by  a  very  fine  silken  thread 
in  the  middle  of  a  glass  body  of  such  size  that  the 
thermometer  with  its  tube  was  entirely  contained  in  it. 


1 98  Historical  Review  of  Experiments 

This  glass  body  was  then  voided  of  air  by  means  of 
mercury. 

The  results  of  the  experiments  performed  with  these 
instruments  differed  little  or  not  at  all  from  those  made 
with  the  apparatus  previously  described,  therefore  the 
fact  of  the  transmission  of  heat  through  the  Torricellian 
vacuum  was  established  beyond  any  doubt. 

These  results  are  sufficiently  known  to  the  learned 
world ;  now  the  question  arises  as  to  how  these  results 
can  be  reconciled  with  the  theory  which  at  the  present 
day  has  been  adopted  in  regard  to  caloric.  I  must  con- 
fess freely,  that,  however  much  I  might  desire  it,  I  never 
could  reconcile  myself  to  it,  because  I  cannot  by  any 
means  imagine  how  heat  can  be  communicated  in  two 
ways  entirely  different  from  each  other. 

Philosophers  have  made  little  or  no  mention  of  the 
results  of  these  investigations  :  I  do  not  assume  to  ex- 
plain their  silence;  if  I  myself  mentioned  them  as  little 
as  they,  it  is  easy  to  imagine  the  cause  of  my  silence. 
It  will  at  least  be  admitted  that  I  have  pointed  out 
plainly  enough  the  doubts  which  the  results  of  my  ex- 
periments could  give  rise  to. 

I  afterwards  undertook  many  other  experiments  to 
determine  accurately  the  various  degrees  of  rapidity 
with  which  heat  passes  into  mercury  when  surrounded 
by  common  or  atmospheric  air,  by  air  saturated  with 
moisture,  by  carbonic  acid  gas,  and  by  air  brought  to 
various  degrees  of  density. 

In  the  year  1787  I  made  a  series  of  experiments 
which  are  described  in  the  Philosophical  Transactions 
for  1792;  my  principal  object  was  to  investigate  the 
conducting  power  with  regard  to  heat  possessed  by  vari- 
ous substances,  especially  by  those  which  we  are  accus- 


on  the  Subject  of  Heat.  1 99 

tomed  to  use  for  clothing.  The  instrument  which  I 
used  in  these  experiments,  and  which  I  called  a  passage- 
thermometery  differs  but  slightly  from  that  described 
above.  I  fixed  the  bulb  of  a  mercurial  thermometer 
half  an  inch  in  diameter  within  a  glass  globe  an  inch 
and  a  half  in  diameter,  with  a  long  cylindrical  neck ; 
I  then  filled  the  space  between  the  outer  surface  of  the 
thermometer  bulb  and  the  inner  surface  of  the  glass 
globe  with  a  certain  quantity  of  the  substance  whose 
conducting  power  was  to  be  determined,  and  allowed 
the  instrument  to  cool  in  a  mixture  of  pounded  ice  and 
water.  As  soon  as  the  thermometer  showed  me  that 
its  bulb  (which  was  in  the  middle  of  the  glass  globe) 
had  acquired  and  retained  constantly  the  temperature 
of  the  cooling  mixture  (that  is,  o°  of  Reaumur's  scale), 
I  took  the  apparatus  out  of  this  cold  mixture,  plunged 
it  into  boiling  water,  observed  the  times  required  for 
the  heat  to  pass  into  the  bulb  of  the  thermometer 
through  the  surrounding  substance,  and  inserted  them 
in  a  table,  noting  every  ten  degrees  as  accurately  as 
possible. 

Since  the  water  into  which  I  plunged  my  appara- 
tus was  kept  constantly  boiling,  it  is  evident  that  the 
outside  of  the  instrument,  that  is,  the  outer  surface  of 
the  globe,  was  always  of  the  same  temperature  ;  hence 
the  more  or  less  rapid  heating  of  the  thermometer 
bulb  within  the  globe  indicated  the  resistance  which 
the  covering  of  the  bulb  offered  to  the  passage  of 
the  heat  from  the  inner  surface  of  the  globe  to  the  bulb 
of  the  thermometer. 

In  this  way  I  made  several  experiments;  but  as  I 
was  inconvenienced  by  the  steam  rising  from  the  boil- 
ing water,  and  so  experienced  difficulty  in  noting  the 


2OO  Historical  Review  of  Experiments 

rising  and  falling  of  the  mercury,  I  changed  my  method 
of  operation,  and  no  longer  observed  the  time  neces- 
sary for  the  instrument  to  grow  warm,  but  that  neces- 
sary for  it  to  grow  cold.  . 

When,  therefore,  my  apparatus,  plunged  in  boiling 
water,  had  acquired  such  a  temperature  that  the  mercury 
had  reached  77°  of  Reaumur's  scale,  I  took  it  out  of 
the  boiling  water  and  held  it  in  the  air,  over  the  large 
vessel  filled  with  pounded  ice  and  water,  ready  to  plunge 
it  into  this  cooling  mixture  the  very  moment  that  the 
mercury  had  fallen  to  75°. 

As  soon  as  the  mercury  had  reached  this  division  of 
the  scale,  I  plunged  my  apparatus  immediately  into  the 
cooling  mixture,  and  holding  at  the  same  time  at  my 
ear  a  watch  which  beat  half-seconds  (which  I  carefully 
counted),  I  waited  for  the  moment  when  the  mercury 
had  fallen  to  70°.  I  then  noted  and  recorded  the  time 
elapsed,  and  in  the  same  way  observed  the  time  when 
the  mercury  had  fallen  to  60°,  and  thus  proceeded, 
noting  every  ten  degrees,  until  the  apparatus  had  cooled 
to  the  temperature  of  10°. 

Sometimes  the  apparatus  cooled  to  such  an  extent 
that  the  mercury  in  the  thermometer  stood  at  o° ;  this, 
however,  took  up  much  time,  and  was  attended  with  no 
particular  advantage,  as  the  determination  of  the  times 
taken  up  in  cooling  from  70°  to  10°  was  quite  sufficient 
for  calculating  the  conducting  power  of  every  sort  of 
covering ;  on  this  account  I  generally  ended  the  experi- 
ment when  the  mercury  had  just  passed  the  10°  mark 
on  the  scale. 

During  the  time  of  cooling  the  apparatus  in  ice  and 
water,  I  moved  it  about  in  the  mixture  very  slowly 
and  constantly  from  one  place  to  another ;  moreover,  I 


on  the  Subject  of  Heat. 


201 


always  mixed  the  water  with  such  a  quantity  of  ice 
that  the  temperature  of  this  mixture  remained  con- 
stant. • 

Since  in  such  experiments  the  thermometer  bulb  in 
the  middle  of  the  glass  globe  was  entirely  surrounded 
as  well  by  the  air  contained  in  the  globe  as  by  the  sub- 
stances of  which  the  covering  consisted,  I  made  a  few 
experiments  to  determine  the  time  necessary  for  the 
bulb  of  the  thermometer  to  become  cold  again  when  the 
globe  contained  nothing  but  air.  I  thus  learned  that 
when  the  apparatus  previously  warmed  in  boiling  water 
was  plunged  into  the  mixture  of  cold  water  and  pounded 
ice,  it  required  576  seconds  to  cool  from  70°  to  10° 
Reaumur. 

The  following  table  contains  the  results  of  several 
experiments  undertaken  with  a  view  to  determine  the 
relative  warmth  of  various  substances  such  as  are  com- 
monly used  for  clothing. 

I  only  remark,  in  addition,  that  I  always  determined 
the  amount  of  the  substance  by  weight  (16  grains  stand- 
ard weight),  and  endeavoured  to  distribute  it  as  equally 
as  possible  in  the  globe,  and  in  such  a  manner  that  the 
bulb  of  the  thermometer  was  surrounded  by  it. 


Gradual  Loss  of 
Heat. 

Substances  used  for  Covering. 

Air. 

Time 

elapsed 

38' 
46 

59 
80 

122 
231 

Raw 

Silk. 

Sheep's- 
wool. 

Cotton- 
wool. 

Fine 
Lint. 

Time 
elapsed 
80" 

93 
"5 
15° 
218 
376 

Beaver's 
Fur. 

Hare's 
Fur. 

Eider- 
down. 

From  70°  to  60° 
60          50 

50  40 
40  3° 

30  20 

20  10 

Time 
elapsed 

94" 

HO 
133 

185 

273 
489 

Time 
elapsed 

79'' 
95 
118 
162 
238 
426 

elapsed. 
83" 

95 
117 

152 

221 
378 

Time 
elapsed. 
99" 
116 

153 
1  8S 
265 
478 

Time 
elapsed. 

97" 
117 
144 

193 

270 

494 

Time 
elapsed. 

98" 
116 
146 
192 

268 
485 

From   70°  to   10° 

576 

1284 

Jii8 

1046 

1032      1296 

'3'5 

'  .V-5 

202  Historical  Review  of  Experiments 


In  order  to  determine  what  influence  the  density  of 
a  covering  or  clothing  of  a  given  thickness  exerted  on 
the  warmth  of  this  covering  or  on  its  power  to  confine 
heat,  I  made  three  consecutive  experiments  with  differ- 
ent quantities  of  one  and  the  same  substance,  namely, 
with  eider-down.  For  the  first  experiment  I  took  16 
grains  of  this  substance,  for  the  second  32  grains,  and 
for  the  third  64  grains.  In  all  cases  I  used  the  same 
apparatus,  so  that  the  thickness  of  the  covering  always 
remained  the  same. 

The  results  of  these  three  experiments  are  contained 
in  the  following  table. 


The  covering  of 
qua 

Eider-down  consisted  of  the  following 
itities  of  the  substance. 

Loss  of  Heat. 

16  grains. 

32  grains. 

64  grains. 

Time  elapsed 

Time  elapsed. 

Time  elapsed. 

From  70°  to  60° 

97" 

Ill" 

112" 

60         50 

117 

128 

130 

50         40 

MS 

157 

I65 

40         30 

192 

207 

224 

30              20 

267 

304 

326 

20           •   IO 

486 

565 

658 

From  70°  to   10° 

i304 

1472 

1615 

Having  convinced  myself  by  these  experiments  that 
the  density  of  any  covering  or  clothing  exercises  a  very 
considerable  influence  on  its  power  to  confine  heat, 
its  thickness  remaining  the  same,  I  now  sought  to  dis- 
cover what  effect  the  internal  structure  or  constitution 
of  the  covering  has  on  this  power,  its  mean  density  and 
its  thickness  remaining  the  same. 

By  the  expression  internal  structure  I  mean  the  state 
of  division,  whether  fine  or  coarse,  of  the  substance  of 
which  the  covering  consists,  in  the  space  which  it  occu- 
pies. This  substance  may  be  very  fine  and  of  delicate 


on  the  Subject  of  Heat.  203 

texture,  and  may  be  equally  distributed  through  the 
whole  space  occupied  by  it,  —  as  raw  silk,  for  example; 
or  it  may  be  coarser  and  have  larger  interstices, — as, 
for  example,  a  covering  consisting  of  bits  of  stout 
sewing-thread,  or  one  consisting  of  ravellings  of  cloth. 

If  heat  really  passed  through  the  substances  of  which 
the  covering  is  made,  and  if  the  efficiency  of  such  a 
covering  in  restraining  the  same  depended  solely  on  the 
greater  or  less  difficulty  which  the  heat  meets  in  passing 
through  the  solid  parts  of  the  covering,  in  that  case 
the  warmth  of  a  covering  would  be,  c<eteris  paribus,  the 
same  as  that  of  the  raw  materials  employed  in  its  con- 
struction. It  is  evident,  however,  from  the  foregoing 
experiments,  as  well  as  from  those  to  be  detailed  here- 
after, that  heat  is  not  propagated  in  any  such  manner. 

In  one  of  my  previous  experiments  I  had  endeav- 
oured to  determine  the  warmth  of  16  grains  of  raw 
silk,  which  I  had  distributed  equally  in  a  certain  space 
about  the  bulb  of  a  thermometer.  I  now  repeated  this 
experiment  twice,  but  with  this  difference :  the  first 
time  I  surrounded  the  bulb  of  the  thermometer  with 
1 6  grains  of  a  sort  of  lint  made  from  a  piece  of 
white  taffety ;  the  second  time  with  16  grains  of  white 
sewing-silk,  cut  into  small  pieces,  two  inches  long.  The 
results  of  these  experiments  are  recorded  in  the  fol- 
lowing table.  My  apparatus  was  warmed  in  boiling 
water,  and  then  cooled  in  a  mixture  of  water  and 
pounded  ice. 


204 


Historical  Review  of  Experiments 


Substances  of  which  the  Covering  consisted. 

Loss  of  Heat. 

Raw  Silk, 

Ravellings  of  Taf- 

Silk  Threads, 

16  grains. 

fety,  16  grains. 

16  grains. 

Time  elapsed. 

Ti  me  elapsed. 

Time  elapsed. 

From  70°  to  60° 

94" 

90" 

67" 

60            50 

no 

106 

79 

50            40 

133 

128 

99 

40            30 

185 

172 

135 

30               20 

273 

246 

195 

20               10 

489 

427 

342 

From  70°  to  10° 

1284 

1169 

917 

Having  convinced  myself  by  these  experiments  that 
the  fineness  of  the  particles  or  fibres  of  the  substance 
used  as  a  covering  contributes  very  much  to  the  warmth 
of  the  same,  I  made  the  following  experiments  to 
determine  what  effect  the  condensing  of  the  covering 
would  have,  the  quantity  of  matter  of  which  it  was  com- 
posed remaining  the  same,  but  the  thickness  being 
decreased. 

As  I  had  already,  by  means  of  the  foregoing  experi- 
ments, determined  the  warmth  of  coverings  of  raw 
silk,  wool,  cotton,  and  linen  when  taking  16  grains 
of  each  substance,  and  making  thereof,  about  the  bulb 
of  a  thermometer,  a  globular  covering  half  an  inch 
thick,  I  now  took  16  grains  of  moderately  coarse 
threads  of  each  of  these  four  substances,  and  with  them 
I  made  four  new  experiments. 

Instead  of  filling  with  these  threads  the  entire  space 
between  the  bulb  of  the  thermometer  and  the  inner 
surface  of  the  globe,  in  the  middle  of  which  was  the 
bulb,  I  wound  it  around  the  bulb  of  the  thermom- 
eter, so  that  the  latter  looked  exactly  like  a  little 
ball. 

I  now  introduced,  as  before,  the  thermometer  bulb 


on  the  Subject  of  Heat. 


205 


thus  enveloped,  into  the  middle  of  a  glass  globe  an  inch 
and  a  half  in  diameter ;  to  this  globe  was  attached  a  neck 
ten  inches  long,  and  of  such  a  width  as  to  allow  of  the 
insertion  of  the  bulb  of  the  thermometer  wrapped  up 
as  described  above,  together  wich  the  attached  scale. 

The  results  of  these  four  experiments  may  be  seen 
in  the  following  table;  and  that  they  may  the  more 
easily  be  compared  with  those  made  with  the  same 
quantity  of  the  substances,  but  differently  disposed,  I 
have  placed  side  by  side  the  results  of  the  comparative 
experiments. 


The  Bulb  of  the  Thermometer  was  covered  with  16  grains 

oi  one  of  the  following  substances. 

Loss  of  Heat. 

Silk. 

Wool 

Cotton. 

Linen. 

Raw. 

threads. 

Raw. 

threads. 

Raw. 

In 

threads. 

Raw. 

threads. 

From  70°  to  60° 

94" 

46" 

79" 

46" 

83" 

45" 

80" 

46" 

60          50 

no 

62 

95 

63 

95 

60 

93 

62 

50       40 

133 

»5 

118 

89 

117 

83 

"5 

83 

40       30 

185 

121 

162 

126 

152 

"5 

150 

H7 

30          20 

273 

I9I 

238 

20O 

221 

179 

218 

180 

20               IO 

489 

399 

426 

4IO 

378 

370 

376 

385 

From   70°  to   10° 

1284 

904 

mS 

934 

1046 

852 

1032 

873 

It  would  carry  me  too  far  if  I  brought  forward 
in  detail  all  the  experimental  results  obtained  in  my 
researches  undertaken  to  investigate  the  manner  in 
which  heat  propagates  itself  through  the  various  cov- 
erings. In  my  printed  memoirs  I  have  said  all  upon 
this  subject  that  can  with  reason  be  said.  For  the 
present  I  have  indicated  clearly,  not  only  the  course 
upon  which  I  entered  at  the  very  beginning  of  my  re- 
searches, but  also  the  object  I  had  in  view.  Philos- 
ophers may  decide  whether  this  course  was  the  right 


206  Historical  Review  of  Experiments 

one,  and  whether  I  pursued  it  with  zeal  and  persever- 
ance. 

The  few  remarks  and  observations  which  follow  were 
occasioned  by  my  researches  made  at  that  time.* 

All  the  different  substances  which  I  had  yet  made  use 
of  for  covering  the  bulb  of  the  thermometer  (which 
was  contained  within  a  glass  globe  an  inch  and  a  half 
in  diameter)  had  in  a  greater  or  less  degree  confined 
the  heat  and  prevented  it  from  passing  into  or  out 
of  the  bulb  of  the  thermometer  as  rapidly  as  it  would 
otherwise  have  done.  Here  then  arose  the  important, 
and  as  yet  unanswered  question,  how  and  by  what 
mechanical  operation  had  the  coverings  in  question  pro- 
duced these  effects  ? 

This  much  is  certain,  that  the  slowness  of  the  cooling 
of  the  bulb  of  the  thermometer  cannot  by  any  possibil- 
ity be  a  result  of  the  non-conducting  powers  of  those 
substances  of  which  the  coverings  consisted,  consid- 
ered simply  as  having  hindered  the  passage  of  the  heat, 
for  if,  instead  of  regarding  them  merely  as  bad  conduc- 
tors of  heat,  we  were  to  suppose  them  to  have  been 
totally  impervious  to  heat,  still  their  volumes  —  that 
is,  the  sum  of  all  their  solid  parts  or  fibres  —  would 
be  so  inconsiderable  in  proportion  to  the  space  they 
occupied,  that  they  would  either  have  produced  no 
effect  on  the  air  filling  their  interstices,  or  this  air  would 
have  been  sufficient  of  and  for  itself  to  have  conducted 
all  the  heat  communicated  in  less  time  than  was  actually 
taken  up  in  the  experiments.  Here  is  the  proof  of  this 
statement. 

The  diameter  of  the  glass  globe  being  1.6  inches,  its 
contents  amounted  to  2.14466  cubic  inches.  The  di- 

*  See  my  eighth  Essay,  Vol.  I.  p.  455. 


on  the  Subject  of  Heat.  207 

ameter  of  the  thermometer  bulb  was  0.55  of  an  inch, 
and  its  contents  0.08711  of  a  cubic  inch.  Taking  now 
from  the  contents  of  the  globe  (2.14466  cubic  inches) 
the  contents  of  the  thermometer  bulb  (0.0871 1  of  a  cubic 
inch),  there  remain  2.05755  cubic  inches  as  the  measure 
of  the  space  occupied  by  the  substances  by  which  the 
bulb  of  the  thermometer  was  surrounded. 

Although  the  above-mentioned  substances  occupied 
this  space,  they  were  very  far  from  filling  it,  as  will  be 
observed  without  my  calling  attention  to  the  fact ;  on 
the  contrary,  this  space  contained  a  large  quantity  of 
air,  which  occupied  and  filled  the  small  interstices  of 
the  substances  in  question. 

For  example,  in  one  of  the  experiments  the  bulb  was 
covered  with  16  grains  of  raw  silk.  As  I  had  already 
learned  from  experiment  that  the  specific  gravity  of  the 
silk  was  to  that  of  water  as  1734  to  1000,  it  follows  that 
the  volume  of  16  grains  of  silk  was  equal  to  the  volume 
of  9.4422  grains  of  water.  Further,  as  I  cubic  inch  of 
water  weighs  253.185  grains,  it  follows  incontrovertibly 
that  the  space  occupied  by  9.4422  grains  of  water  can  be 
reckoned  at  the  highest  at  0.037294  of  a  cubic  inch,  and 
this  amount  of  water  (9.4422  grains)  corresponds  in 
volume  to  1 6  grains  of  silk. 

We  know,  however,  that  the  space  which  this  small 
quantity  of  silk  (0.037294  of  a  cubic  inch)  occupies  is 
2.05755  cubic  inches;  hence  it  appears  that,  since 
0.037294  is  to  2.05755  as  i  is  to  54,  the  silk  which  I 
used  in  the  experiment  in  question  could  not  fill  more 
than  -5^  of  the  space  in  which  it  was  confined. 

The  longer  we  meditate  upon  these  investigations, 
the  more  we  are  struck  by  the  importance  of  the 
results  that  follow  from  them.  I  have  never  been 


208  Historical  Review  of  Experiments 

able  to  explain  them  without  rejecting  altogether  that 
hypothesis  according  to  which  it  is  supposed  that  the 
heat  which  may  be  in  the  air  is  communicated  directly 
from  one  particle  of  this  fluid  to  another. 

My  researches  on  the  propagation  of  heat  in  liquids 
are  sufficiently  well  known.*  From  them  it  has  prob- 
ably been  seen  how  and  in  what  manner  I  was  com- 
pelled by  the  results  of  my  numerous  experiments  to 
adopt  the  opinion  with  regard  to  this  subject  which  I 
have  developed  in  my  various  writings. 

I  have  examined  with  the  greatest  care  the  objections 
which  have  been  offered  to  the  deductions  which  I  have 
drawn  from  my  experiments,  and  I  can  assert  with 
truth  —  and  to  say  this  is  a  duty  I  owe  to  myself — 
that  neither  in  these  objections  nor  in  the  result  of  any 
new  experiment,  as  far  as  my  knowledge  extends,  has 
the  least  thing  occurred  which  could  serve  as  a  reason 
for  altering  my  opinion  in  regard  to  this  subject.  In 
a  paper  which  I  sent  last  year  to  the  Royal  Society 
at  London,-]-  I  think  that  I  have  proved  that  water  is 
really  a  non-conductor  of  heat,  as  I  suspected  six  years 
ago. 

I  have  now  only  a  few  words  to  say  in  addition, 
about  the  various  experiments  which  I  made  at  different 
times,  to  enable  me  (if  it  were  in  any  way  possible)  to 
answer  decisively  that  important  and  much  contested 
question  as  to  the  materiality  of  heat,  about  which 
philosophers  have  striven  for  so  long  a  time. 

Those  who  regard  heat  as  a  substance  must,  of 
necessity,  assume  that  it  possesses  weight.  If  now  the 

*  A  detailed  description  of  my  investigations  in  regard  to  this  interesting  subject  is 
contained  in  my  seventh  Essay,  which  appeared  in  London  in  the  year  1797,  in  two 
parts,  together  188  octavo  pages.  See  also  Vol.  I.  p.  239. 

f  See  p.  274. 


on  the  Subject  of  Heat.  209 

heating  of  a  body  is  caused  by  the  accumulation  of  this 
substance  in  the  body,  it  follows  naturally  that  the 
body  must  be  heavier  when  it  is  warm  than  when  it  is 
cold.  Some  natural  philosophers  have  sought  to  deter- 
mine this  point ;  I  feel  confident,  however,  that  no  one 
has  made  more  decisive  experiments  in  this  direction 
than  myself.* 

I  was  provided  with  excellent  instruments,  and  spared 
neither  trouble  nor  expense  to  arrive,  by  means  of  my 
experiments,  at  a  certain  and  convincing  result.  The 
results  obtained  are,  in  few  words,  as  follows. 

I  had  a  ball  of  very  fine  gold  made,  and  weighed  it 
when  perfectly  cold,  and  again  after  heating  it  to  such  a 
temperature  that  it  was  on  the  point  of  melting.  Fur- 
ther, I  weighed  a  considerable  amount  of  water,  which  I 
had  sealed  hermetically  in  a  flask,  first  in  its  liquid 
state,  then  at  the  temperature  of  melting  ice,  then  as 
actual  ice,  and  then  again  at  its  original  temperature. 
All  these  experiments  convinced  me  that  the  weight 
of  a  body  is  not  changed  in  the  least  by  heat. 

Now  although,  as  a  consequence  of  the  results  of 
these  experiments,  I  was  only  still  more  strengthened  in 
those  doubts  which  a  number  of  other  natural  phenom- 
ena had  raised  in  my  mind  with  regard  to  the  existence 
of  caloric,  still  I  saw  at  the  same  time  only  too  well 
that  the  essential  point  of  the  controversy  was  far  from 
being  decided  thereby.  The  defenders  of  caloric  would 
still  object  (as  they  have  actually  done)  that  this  sub- 
stance is  far  too  subtile  to  be  weighed  upon  our  ordi- 
nary balances. 

*  A  paper  in  which  are  described  in  detail  all  my  experiments  upon  this  sub- 
ject may  be  found  in  the  Philosophical  Transactions  for  1799.  See  also  page  1  ot  this 
volume. 

VOL.   II.  14 


2io  Historical  Review  of  Experiments 

After  I  had  long  meditated  upon  a  way  of  putting 
this  interesting  problem  entirely  out  of  doubt  by  a 
perfectly  conclusive  experiment,  I  thought  finally  that 
I  had  discovered  it,  and  I  think  so  still. 

I  argued  that  if  the  existence  of  caloric  was  a  fact,  it 
must  be  absolutely  impossible  for  a  body  or  for  several 
individual  bodies,  which  together  made  one  whole,  to 
communicate  this  substance  continuously  to  various 
other  bodies  by  which  they  were  surrounded,  without 
this  substance  gradually  being  entirely  exhausted. 

A  sponge  filled  with  water,  and  hung  by  a  thread  in 
the  middle  of  a  room  filled  with  dry  air,  communicates 
its  moisture  to  the  air,  it  is  true,  but  soon  the  water 
evaporates  and  the  sponge  can  no  longer  give  out  moist- 
ure. On  the  contrary,  a  bell  sounds  without  inter- 
ruption when  it  is  struck,  and  gives  out  its  sound  as 
often  as  we  please  without  the  slightest  perceptible  loss. 
Moisture  is  a  substance ;  sound  is  not. 

It  is  well  known  that  two  hard  bodies,  if  rubbed  to- 
gether, produce  much  heat.  Can  they  continue  to  pro- 
duce it  without  finally  becoming  exhausted  ?  Let  the 
result  of  experiment  decide  this  question. 

It  would  be  too  tedious  to  describe  here  in  detail 
all  the  experiments  which  I  undertook  with  a  view 
of  answering  in  a  decisive  manner  this  important  and 
disputed  question.  They  may  be  found  in  my  memoir 
On  the  Source  of  Heat  excited  by  Friction.  I  have 
had  it  printed  in  the  Philosophical  Transactions  for 
the  year  1798  ;  still  these  experiments  bear  too  close  a 
relation  to  my  later  researches  on  heat  for  me  to  omit 
attempting  at  least  to  give  the  reader  a  clear  idea  of  the 
experiments  and  of  their  results. 

The  apparatus  which  I  used  in  these  investigations 


on  the  Subject  of  Heat.  211 

is  too  complicated  to  be  represented  in  this  place ;  * 
still  it  will  not  be  difficult  for  the  reader,  with  the 
help  of  the  accompanying  figure  (see  Plate  V.),  to 
form  a  conception  of  the  principal  experiments  and 
their  results. 

Let  A  be  the  vertical  section  of  a  brass  rod  which  is 
an  inch  in  diameter  and  is  fastened  in  an  upright  posi- 
tion on  a  stout  block,  B  ;  it  is  provided  at  its  upper 
end  with  a  massive  hemisphere  of  the  same  metal,  three 
and  a  half  inches  in  diameter.  C  is  a  similar  rod,  like- 
wise vertical,  to  the  lower  end  of  which  is  fastened  a 
similar  hemisphere.  Both  hemispheres  must  fit  each 
other  in  such  a  way  that  both  the  rods  stand  in  a  per- 
fectly straight  vertical  line. 

D  is  the  vertical  section  of  a  globular  metallic  vessel 
twelve  inches  in  diameter,  which  is  provided  with  a 
cylindrical  neck  three  inches  long  and  three  and  three- 
quarters  inches  in  diameter.  The  rod  A  goes  through 
a  hole  in  the  bottom  of  the  vessel,  is  soldered  into  the 
vessel,  and  serves  as  a  support  to  keep  it  in  its  proper 
position. 

The  centre  of  the  ball,  made  up  of  the  two  hemi- 
spheres which  lie  the  one  upon  the  other,  is  in  the 
centre  of  the  globular  vessel,  so  that,  if  the  vessel  is  filled 
with  water,  the  water  covers  the  ball  as  well  as  a  part 
of  each  of  the  brass  rods. 

If  now  the  hemispheres  be  pressed  strongly  together, 
and  at  the  same  time  the  rod  C  be  turned,  by  some 
means  or  other,  about  its  axis,  a  very  considerable 
quantity  of  heat  is  generated  by  means  of  the  friction 
which  takes  place  between  the  flat  surfaces  of  the  two 
hemispheres. 

*  See  Vol.  I.,  Plate  to  p.  493. 


2 1 2  Historical  Review  of  Experiments 

The  quantity  of  the  heat  excited  in  this  manner  is 
exactly  proportional  to  the  force  with  which  the  two 
surfaces  are  pressed  together,  and  to  the  rapidity  of  the 
friction.  When  this  force  was  equal  to  the  pressure  of 
ten  thousand  pounds,  and  when  the  rod  was  turned 
with  such  rapidity  about  its  axis  that  it  revolved  thirty- 
two  times  a  minute,  the  quantity  of  heat  generated  by 
the  continual  rubbing  of  the  two  surfaces  together  was 
extraordinarily  great.  It  was  equal  to  the  quantity  given 
off  by  the  flame  of  nine  wax-candles  of  moderate  size 
all  burning  together. 

The  quantity  of  heat  generated  in  this  manner  dur- 
ing a  given  time  is  manifestly  the  same,  whether  the 
globular  vessel  D  is  filled  with  water,  and  the  surfaces 
of  the  two  hemispheres  rub  on  each  other  in  this  liquid, 
or  whether  there  is  no  water  in  the  vessel,  and  the  ap- 
paratus by  which  the  friction  is  produced  is  simply  sur- 
rounded by  air. 

The  source  of  the  heat  which  is  generated  by  this 
apparatus  is  inexhaustible.  As  long  as  the  rod  C  is 
turned  about  its  axis,  so  long  will  heat  be  produced  by 
the  apparatus,  and  always  to  the  same  amount. 

If  the  globe-shaped  vessel  D  is  filled  with  water,  this 
water  becomes  hotter  and  hotter,  and  finally  begins  to 
boil.  I  have  myself  in  this  way  boiled  a  considerable 
quantity  of  water. 

If  this  experiment  is  performed  in  winter  when  the 
temperature  of  the  air  is  but  little  above  the  freezing- 
point,  and  if  the  vessel  D  is  filled  with  a  mixture  of 
water  and  pounded  ice,  the  quantity  of  heat  caused 
in  a  given  time  by  the  rubbing  together  of  the  two  sur- 
faces can  be  expressed  very  exactly  by  the  amount  of 
ice  melted  by  this  heat. 


on  the  Subject  of  Heat.  213 

Since  the  apparatus  affords  heat  continuously,  and 
always  to  the  same  amount,  we  can  melt  in  this  way  as 
much  ice  as  we  please. 

But  whence  comes  this  heat  ?  This  is  the  contested 
point,  to  determine  which  was  the  real  aim  of  the  ex- 
periment. 

It  is  certain  that  it  comes  neither  from  the  decom- 
position cf  the  water  nor  from  the  decomposition  of  the 
air  Various  experiments  on  this  point,  which  I  have 
described  at  length  in  my  memoir  in  the  Philosophical 
Transactions,  are  more  than  sufficient  to  establish  this 
fact  beyond  doubt. 

Just  as  little  does  it  come  from  a  change  in  the  ca- 
pacity for  heat  brought  about  by  friction  in  the  metal 
of  which  the  hemispheres  are  composed.  This  is  shown, 
first,  by  the  continuance  and  uniformity  of  the  pro- 
duction of  the  heat ;  and,  secondly,  by  an  experiment 
bearing  directly  on  this  point,  by  which  I  am  con- 
vinced that  not  the  slightest  change  had  taken  place  in 
the  capacity  of  the  metal  for  heat. 

Just  as  little  does  it  come  from  the  rods  which 
are  attached  to  the  hemispheres,  for  these  rods  were 
always  warm,  the  hemispheres  communicating  heat  to 
them. 

Much  less  could  this  heat  come  from  the  air  or  the 
water  immediately  surrounding  the  hemispheres,  for  the 
apparatus  communicated  heat  to  both  these  fluids  with- 
out cessation. 

Whence,  then,  came  this  heat?  and  what  is  heat 
actually? 

I  must  confess  that  it  has  always  been  impossible  for 
me  to  explain  the  results  of  such  experiments  except  by 
taking  refuge  in  the  very  old  doctrine  which  rests  on 


214  Historical  Review  of  Experiments 

the  supposition  that  heat  is  nothing  but  a  vibratory 
motion  taking  place  among  the  particles  of  bodies. 

A  bell,  on  being  struck,  immediately  gives  forth  a 
sound,  and  the  oscillations  of  the  air  produced  by  these 
vibrations  forthwith  cause  a  quivering  motion  in  those 
bodies  with  which  they  come  in  contact.  On  the  other 
hand,  a  sponge  filled  with  water  cannot  give  ofF  its 
moisture  to  the  bodies  in  its  vicinity  for  any  length  of 
time  without  itself  losing  moisture. 

A  very  illustrious  philosopher,  for  whom  I  have  al- 
ways entertained  the  greatest  respect,  and  whom,  more- 
over, I  have  the  good  fortune  to  count  among  my  most 
intimate  friends,  M.  Bertholet,  has,  in  his  admirable 
Essai  de  Statique  Chimique,  attempted  to  explain  the  re- 
sults of  this  investigation,  and  to  reconcile  them  with 
that  theory  of  heat  which  is  founded  upon  the  hypothe- 
sis of  caloric. 

If  a  man  as  learned,  as  honest,  as  worthy,  and  as  re- 
nowned as  is  M.  Bertholet,  spares  no  pains  in  opposing 
the  errors  of  a  natural  philosopher  or  chemist,  one  can- 
not and  dare  not  keep  silence  unless,  he  wishes  to  ac- 
knowledge himself  vanquished.  If,  however,  one  can 
produce  proofs  —  a  fortunate  thing  for  all  those  who 
find  themselves  driven  to  similar  self-vindication  —  that 
the  objections  of  M.  Bertholet  have  no  foundation,  he 
has  done  very  much  towards  establishing  beyond  doubt 
the  opinions  and  facts  in  question. 

I  will  now  endeavour  to  answer  the  objections  which 
M.  Bertholet  has  offered  to  my  explanation  of  the 
above-mentioned  experiments  ;  and,  that  the  reader 
may  be  in  a  position  to  give  to  these  objections  their 
just  value,  I  will  insert  them  here  in  the  writer's  own 
words. 


on  the  Subject  of  Heat.  2 1 5 

"Count  Rumford  has  made  a  curious  experiment 
with  regard  to  the  heat  which  may  be  excited  by  fric- 
tion. He  causes  a  blunt  borer  to  revolve  very  rapidly 
(this  borer  revolved  about  its  axis  only  thirty-two  times  a 
minute}  in  a  brass  cylinder  weighing  thirteen  pounds, 
English  weight  (the  cylinder  weighed  one  hundred  and 
thirteen  pounds  and  somewhat  more\  and  says  that  he 
observed  that  this  borer  in  the  course  of  two  (one  ana 
a  half)  hours,  and  under  a  pressure  equal  to  100 
cwt.,  reduced  to  powder  4145  grains  (8J  ounces  Troy) 
of  brass,  and  that  an  amount  of  heat  was  generated 
during  this  operation  sufficient  to  bring  to  boil  26.38 
pounds  of  water,  previously  cooled  to  the  freezing- 
point.  He  asserts  that  he  did  not  discover  the  slight- 
est difference  between  the  specific  heat  of  the  metallic 
dust  and  that  of  the  brass  which  had  not  experienced 
the  friction.  Hence  he  supposes  that  the  heat  was 
excited  by  the  pressure  alone,  and  was  not  at  all  due  to 
caloric,  as  is  the  opinion  of  most  chemists. 

"  I  will  for  the  present  satisfy  myself  with  simply 
inquiring  whether  it  necessarily  follows  from  this  ex- 
periment that  we  must  renounce  entirely  the  received 
theory  of  caloric,  according  to  which  it  is  regarded  as 
a  substance  which  enters  into  combination  with  bodies, 
or  whether  this  result  cannot  be  explained  in  a  satis- 
factory manner  by  applying  to  the  case  in  question 
those  laws  of  nature  in  accordance  with  which  the  opera- 
tions of  heat  are  manifested  under  other  conditions. 

"If  the  evolution  of  heat  be  regarded  as  a  conse- 
quence of  the  decrease  of  volume  caused  by  the  pressure, 
then  not  only  the  metallic  powder  but  also  all  the  rest 
of  the  brass  cylinder  must  have  contributed,  though  not 
in  an  equal  manner,  to  this  evolution,  by  the  powerful 


2 1 6  Historical  Review  of  Experiments 

expansive  effort  of  that  portion  which  experienced  the 
greatest  pressure,  and  consequently  acquired  the  greatest 
temperature,  without  being  able  to  assume  the  dimen- 
sions proper  to  this  same  temperature  on  account  of 
the  less  heated  and  less  expanded  parts ;  consequently 
there  must  have  arisen,  necessarily,  a  certain  condensa- 
tion of  the  metal  in  respect  of  its  natural  dimensions, 
which  condensation  gradually  decreased  from  the  point 
where  the  pressure  was  greatest  to  the  surface.  We  may 
suppose  that  this  operation  took  place  in  a  similar  man- 
ner in  all  parts  of  the  cylinder. 

"As  a  consequence  of  this  decrease  of  volume,  an 
amount  of  caloric  was  given  out  equal  to  that  which 
would  have  caused  a  similar  increase  of  volume,  on  the 
supposition,  that  is,  that  the  specific  heat  of  the  metal 
does  not  change  through  this  range  of  the  scale  of  the 
thermometer,  and  that  the  expansions  are  equal ;  and 
this,  considering  the  range  of  temperatures  and  the 
consequent  expansions,  is  probably  not  far  from  the 
truth.  The  entire  amount  of  heat  disengaged  would 
have,  raised  the  cylinder  to  about  1 80°  of  Reaumur's 
scale;  and  if  the  expansion  of  brass  by  heat  is  equal 
to  that  of  iron,  which  has  been  found  to  be  y^o"o  f°r 
each  degree  of  the  thermometer,  the  180  degrees  would 
have  caused  an  expansion  of  y-^f -5-  in  each  direction,  and 
the  decrease  of  volume  must  have  brought  about  the 
same  degree  of  heat  if  we  suppose  that  the  pressure 
stood  in  equal  relation  to  this  expansion. 

"  Now  there  is  a  change,  and  sometimes  a  very  consid- 
erable one,  wrought  in  the  specific  gravity  of  a  metal, 
by  percussion,  by  the  action  of  a  fly-wheel,  or  by  the 
compression  of  a  wire-drawing  machine.  It  appears, 
for  example,  that  the  specific  gravity  of  platina  and  of 


on  the  Subject  of  Heat.  2 1 7 

iron,  on  being  forged,  is  thus  increased  by  a  twentieth 
part. 

"  Hence  it  appears  that  the  experiment  of  Count 
Rumford  is  far  from  explaining  satisfactorily  a  property 
which  is  well  known,  and  called  in  question  by  no 
one. 

"  It  is  easy,  it  is  true,  to  arrange  side  by  side  in 
an  imposing  manner  the  phenomena  of  heat ;  if,  how- 
ever, you  were  to  say  to  one  who  has  little  or  no 
knowledge  of  chemical  speculations,  *  Count  Rumford's 
cylinder  has,  in  the  course  of  two  hours,  by  means  of 
a  violent  friction,  afforded  all  the  heat  required  to  dis- 
solve in  water,  without  changing  its  temperature,  15 
kilogrammes  of  ice,  or  as  much  as  2  hectogrammes  (6| 
ounces)  of  oxygen  would  require  [sic]  in  its  combina- 
tion with  phosphorus,'  I  do  not  know  at  which  of 
these  phenomena  he  would  be  most  astonished. 

"  The  slight  changes  which  can  take  place  in  the 
amount  of  combined  caloric  have  so  inconsiderable  an 
influence  on  the  capacity  for  work  of  the  caloric  within 
the  narrow  limits  of  the  thermometric  scale,  that  it 
cannot  be  computed.  Moreover,  we  have  not,  as 
yet,  adequate  data  for  determining  the  nature  of  the 
changes  in  this  respect  which  take  place  in  a  solid  body 
in  consequence  of  the  particular  condition  of  condensa- 
tion into  which  it  has  been  brought  by  means  of  a  cer- 
tain mechanical  force,  and  by  degrees  of  heat  differing 
greatly  from  each  other. 

"  Besides,  Rumford,  in  the  experiment  to  determine 
the  specific  heat  of  the  filings  of  bell-metal  thus  ob- 
tained, heated  them  to  the  temperature  of  boiling 
water.  But  this  extremely  elastic  metal  would  very 
naturally  as  soon  as  left  to  itself,  and  especially  dur- 


2 1 8  Historical  Review  of  Experiments 

ing  the  operation  just  mentioned,  resume  that  state  of 
expansion  and  that  capacity  for  heat  which  is  proper 
to  it  at  a  given  temperature,  so  that  the  effect  of  the 
pressure  to  which  it  has  been  subjected  partly  disap- 
pears again,  just  as  a  piece  of  metal  which  has  been 
hammered  resumes  its  natural  properties  on  being  an- 
nealed." 

In  reply  to  these  remarks,  I  will  call  to  mind  what 
follows. 

ist.  The  discovery  which  I  made,  that  no  consid- 
erable change  had  taken  place  in  the  specific  heat  of 
the  metallic  dust  produced  by  the  friction,  led  me  in 
no  way  to  the  supposition  that  the  heat  excited  in  the 
experiment  could  not  come  from  the  caloric  set  free. 
I  only  found  that  the  source  of  this  heat  was  inex- 
haustible. To  explain  this  phenomenon,  which  has 
never  yet  been  explained,  is  the  point  now  in  ques- 
tion, and  I  do  not  see  how  it  can  be  explained  except 
by  giving  up  altogether  the  hypothesis  adopted  in  re- 
gard to  caloric. 

id.  If  we  actually  suppose  (and  it  is  far  from  having 
been  proved)  that  the  simple  pressing  together  of  a 
metal  is  sufficient  to  expel  the  caloric  contained  in  it, 
still  the  explanation  of  such  a  natural  phenomenon 
would  be  advanced  little  or  none;  for  since  the  action 
of  the  force  which  causes  the  pressure  is  continuous,  the 
condensation  of  the  metal  brought  about  by  this  force 
would  in  a  short  time  reach  its  maximum  ;  and  if 
really  in  this  operation  ever  so  much  caloric  had  been 
disengaged  from  the  metal,  still  it  would  very  soon 
disperse.  The  rubbing  surfaces,  on  the  contrary,  con- 
tinue to  give  forth  heat,  and  that  always  to  the  same 
amount. 


on  the  Subject  of  Heat.  2 1 9 

3d.  In  regard  to  the  objection  made  to  the  experi- 
ment which  was  undertaken  with  a  view  of  determin- 
ing whether  a  change  had  taken  place  in  the  capacity 
of  the  metallic  dust  for  heat,  this  can  very  readily  be 
answered,  and  in  such  a  way  that  nothing,  it  seems  to 
me,  can  be  said  against  it.  If  the  temperature  of  boil- 
ing water  were  really  sufficient  to  give  to  these  small, 
forcibly  condensed  particles  of  metal  the  quantity  of 
heat  necessary  to  bring  them  back  to  their  original  con- 
dition as  far  as  their  capacity  for  heat  is  concerned,  then, 
as  the  water  by  which  the  apparatus  was  surrounded 
finally  began  to  boil,  they  must,  without  doubt,  have 
taken  the  necessary  amount  of  heat  from  this  water.  If, 
now,  these  particles  of  metal  received  finally  from  the 
water  the  caloric  which  in  the  beginning  they  imparted 
to  it,  the  question  arises,  whence  came  the  caloric  which 
served  to  heat,  not  only  the  water,  but  also  the  metal 
and  the  objects  immediately  surrounding  it  ? 

I  am  far  from  desiring  to  deceive  any  one  by  an  im- 
posing arrangement  of  facts ;  but  the  facts  in  my  ex- 
periments were  so  very  striking  that  it  was  altogether 
impossible  for  me  to  help  instituting  comparisons  and 
making  calculations  with  regard  to  them  which  would 
make  them  clear,  especially  to  those  not  yet  sufficiently 
acquainted  with  such  investigations. 

I  will  now  close  my  remarks  with  an  entirely  new 
computation.  I  will  show  whether  it  is  probable 
that  the  metal  could  supply  all  the  heat  which  was  pro- 
duced by  friction  in  the  experiment  in  question.  If 
we  are  to  make  this  supposition,  we  must,  in  the  first 
place,  allow  that  all  the  heat  came  directly  from  the 
particles  of  metal  which  were  separated  from  the  solid 
mass  of  metal  by  the  friction  ;  for,  since  the  mass  re- 


220  Historical  Review  of  Experiments 

mained  in  the  same  condition  throughout  the  entire 
experiment,  it  is  evident  that  it  could  contribute  in  no 
measure  to  the  effect  produced. 

We  will  now  inquire  how  much  heat  would  have  been 
developed  if  the  experiment  had  been  carried  on  without 
cessation,  until  the  whole  mass  of  metal  had  been  re- 
duced to  powder  by  the  friction. 

After  the  experiment  had  lasted  an  hour  and  a  half, 
there  were  4145  grains  (Troy)  of  the  metallic  dust,  and 
during  that  time  an  amount  of  heat  was  produced  by 
the  friction  sufficient  to  raise  26.58  pounds  of  ice-cold 
water  to  the  boiling-point. 

Since  the  mass  of  metal  weighed  113.13  pounds,  or 
791,910  grains,  all  this  metal  would  have  been  reduced  to 
powder  if  the  experiment  had  lasted  uninterruptedly,  day 
and  night,  for  477^  hours,  or  for  19  days  21^  hours, 
and  during  this  time  an  amount  of  heat  would  have 
been  produced  sufficient  to  have  raised  5078  pounds 
of  water  to  the  boiling-point. 

Since  the  metal  used  in  this  experiment  showed  a 
capacity  for  heat  which  was  to  that  of  water  as  o.n  to 
i,  it  is  evident  that  this  amount  of  heat  would  have 
been  sufficient  to  raise  a  mass  of  the  same  metal  46,165 
pounds  in  weight  through  180  degrees  of  Fahrenheit's 
scale,  or  from  the  temperature  of  melting  ice  to  that  of 
boiling  water. 

This  amount  of  heat  would  be  sufficient  to  melt  a 
mass  of  metal  sixteen  times  heavier  than  that  which  I 
used  in  the  experiment.* 

*  Brass  melts  at  a  temperature  of  3807°  Fahrenheit;  copper  at  4587°;  bell- 
metal  melts  more  easily  than  copper ;  if,  however,  we  suppose  that  it  requires  the 
same  heat  for  fusion,  we  find  by  a  very  simple  calculation,  that  the  amount  of  heat 
necessary  to  raise  the  temperature  of  46,165  pounds  bell-metal  through  180  degrees 
would  'be  sufficient  to  raise  the  temperature  of  i8n£  pounds  through  4587 


on  the  Subject  of  Heat.  221 

Is  it  at  all  conceivable  that  such  an  enormous  quan- 
tity of  caloric  could  really  be  present  in  this  body  ?  But 
even  this  supposition  would  be  by  no  means  sufficient 
for  the  explanation  of  the  fact  in  question,  as  I  have 
shown  by  a  decisive  experiment  that  the  capacity  of  the 
metal  for  heat  has  not  sensibly  altered. 

Whence,  then,  came  the  caloric  which  the  apparatus 
furnished  in  such  abundance  ? 

I  leave  this  question  to  be  answered  by  those  persons 
who  believe  in  the  actual  existence  of  caloric. 

In  my  opinion,  I  have  made  it  sufficiently  evident 
that  it  was  impossible  for  it  to  come  from  the  metallic 
bodies  which  were  rubbed  together,  and  I  am  absolutely 
unable  to  imagine  how  it  can  have  come  from  any  other 
object  in  the  neighbourhood  of  the  apparatus,  for  all 
these  objects  received  their  heat  constantly  from  the 
apparatus  itself. 

I  will  now  proceed  to  give  an  account  of  my  further 
investigations  on  the  subject  of  Heat. 

In  the  summer  of  the  year  1800,  I  visited  Scotland, 
and  on  this  occasion  spent  some  months  in  Edinburgh. 

It  is  well  known  that  the  University  at  that  place 
stands  in  high  repute  on  account  of  the  eminent  scholars 
occupying  chairs  there  for  more  than  fifty  years  in  un- 
interrupted succession. 

One  day  I  found  myself  in  the  company  of  Professor 
Hope  (the  successor  of  the  celebrated  Black),  Professors 
Playfair  and  Stewart,  and  several  other  persons.  We 
repeated  the  experiment  which  Pictet  undertook  with 
a  view  to  determine  the  condensation  and  contraction 

degrees,  or  to  bring  this  number  of  pounds  to  the  melting-point.  From  this  calculation 
it  appears  that  a  quantity  of  bell-metal,  the  temperature  of  which  is  at  the  melting- 
point  of  ice,  on  being  reduced  by  friction  to  the  state  of  powder,  gives  out  sixteen 
times  as  much  heat  as  would  be  necessary  to  melt  it. 


222  Historical  Review  of  Experiments 

of  air  by  the  cooling  influence  of  cold  bodies.  It  now 
happened  that  for  the  first  time  my  opinion  on  the 
subject  of  heat  was  publicly  announced. 

Two  metallic  mirrors  fifteen  inches  in  diameter,  with 
a  focal  distance  of  fifteen  inches,  were  placed  opposite 
each  other,  sixteen  feet  apart.  When  a  cold  body  (for 
example,  a  glass  bulb  filled  with  water  and  pounded 
ice)  as  was  the  case  on  this  occasion,  was  placed  in  the 
focus  of  one  of  the  mirrors,  and  a  very  sensitive  air- 
thermometer  was  placed  in  the  focus  of  the  other  mir- 
ror, the  latter  thermometer  began  immediately  to  fall. 
If,  instead  of  being  placed  directly  in  the  focus,  the 
thermometer  was  removed  a  short  distance  from  it  to 
one  side,  the  cooling  power  which  in  the  former  case  the 
cold  body  had  exerted  upon  it  was  no  longer  perceptible. 

The  matter  was,  however,  not  allowed  to  rest  with 
merely  repeating  the  experiment  of  Pictet  just  as  he 
describes  it,  but  I  was  allowed,  in  addition,  to  make 
various  changes,  that  I  might  lay  aside  every  doubt,  and 
elucidate  in  the  most  convincing  manner  the  fact  in 
question. 

I  expressed  my  opinion  on  the  results  of  these  ex- 
periments in  the  following  words  :  — 

<c  It  is  not  possible  that  caloric  has  an  actual  exist- 
ence. The  communication  of  heat  and  the  communi- 
cation of  sound  seem  to  be  completely  analogous.  The 
cold  body  in  one  focus  compels  the  warm  body  (the 
thermometer)  in  the  other  focus  to  change  its  note? 

It  is  owing  to  a  peculiar  circumstance,  the  further 
discussion  of  which  would  be  neither  appropriate  nor 
useful  in  this  place,  that  I  here  introduce  word  for  word 
the  expression  which  I  used  on  this  occasion. 

A  considerable  time  before,  I  had  already  projected 


on  the  Subject  of  Heat.  223 

a  series  of  experiments  on  the  subject  of  radiant  heat, 
and  in  my  sixth  Essay,  which  treats  Of  the  Manage- 
ment of  Fire  and  the  Economy  of  Fuel,  published  at 
London  in  I797>  I  had  openly  announced  my  purpose 
of  taking  the  work  in  hand  as  soon  as  possible. 

The  experiments  I  have  just  mentioned  as  being 
performed  in  my  presence  by  Professor  Hope  deter- 
mined me  not  to  put  off  this  intention  of  mine  a 
moment  longer. 

As  soon  as  I  returned  to  London,  I  began  imme- 
diately to  make  all  preparations  for  my  researches.  I 
therefore  communicated  my  intentions  to  Sir  Joseph 
Banks,  at  that  time  President  of  the  Royal  Society, 
also  to  Mr.  Cavendish,  because  both  these  gentlemen 
(as  well  as  myself)  were  managers  of  the  Royal  In- 
stitution. As  I  wished  to  carry  out  my  experiments 
in  the  most  decisive  manner,  and  consequently  with 
the  apparatus  as  perfect  as  possible,  —  which  to  all 
appearance  would  require  a  considerable  outlay,  —  I 
was,  at  my  request,  authorized  by  the  managers  of 
the  Royal  Institution  to  procure  the  new  instruments 
needed  at  the  expense  of  the  Institution,  with  the  con- 
dition, however,  that  these  instruments  should  remain 
at  the  Institution  as  its  property,  and  be  kept  in  its 
cabinet. 

As  the  principal  object  in  this  investigation  was  to 
establish  beyond  doubt  the  cooling  emanations  from 
cold  bodies,  I  desired  to  accumulate  the  emanations  and 
concentrate  them  as  much  as  possible,  in  order  that 
their  action  might  be  so  much  the  more  sensible. 

Pictet  took  for  his  experiment,  as  is  well  known,  two 
metallic  reflectors,  and  placed  a  cold  body  in  the  focus 
of  one  of  them,  and  a  thermometer  in  the  focus  of 


224  Historical  Review  of  Experiments 

the  other.  That  the  cooling  influence  which  the  cold 
object  exerted  on  the  thermometer  might  be  doubled, 
I  proposed  in  my  experiment  to  have  two  cold  bodies 
and  one  reflector,  and,  in  order  to  increase  so  much  the 
more  the  cooling  effect  on  the  thermometer,  I  intended 
to  place  it  in  the  upper  part  of  an  open  cylindrical 
vessel,  the  two  cold  bodies,  however,  being  placed  some- 
what lower. 

In  Pictet's  experiments  both  reflectors  were  in  a  hori- 
zontal line,  and  the  thermometer  on  which  the  cooling 
influences  were  exerted  was  continually  heated  by  the 
vertical  current  from  the  air  above,  which  was  caused 
necessarily  by  the  cooling  of  the  stratum  of  air  immedi- 
ately surrounding  the  thermometer;  as  a  consequence, 
the  frigorific  influence  of  the  cold  body  was  lessened  by 
the  calorific  influence  of  this  current  to  such  an  ex- 
tent that  an  equilibrium  resulted.  Still  I  expected  that 
in  my  case  I  should,  in  all  probability,  be  able  to  carry 
the  cooling  of  the  thermometer  still  farther,  as  I  hoped 
by  the  arrangement  of  my  apparatus  to  prevent  this 
current,  and  at  the  same  time  to  double  the  cooling 
effect. 

After  long  delay  on  the  part  of  the  workmen,  the 
necessary  mirrors,  four  in  number,  were  finally  com- 
pleted. They  are  now  in  the  physical  cabinet  of  the 
Royal  Institution  at  London,  and  are  used  in  the  an- 
nual lectures  on  physics.  If  I  am  not  mistaken,  there 
are  several  other  instruments  kept  in  the  same  place, 
which  I  had  expected  to  use  in  the  projected  experi- 
ments on  the  radiation  of  bodies ;  but  most  of  the  in- 
struments designed  for  this  investigation  (made  by  Mr. 
Fraser,  New  Bond  Street)  were  made  at  my  own  ex- 
pense and  are  still  in  my  possession. 


on  the  Subject  of  Heat.  225 

It  is  only  necessary  to  see  this  apparatus,  which  I 
had  made  in  the  summer  of  1801,  to  be  immediately 
convinced  that  I  pursued  my  researches  on  the  subject 
of  heat  zealously  and  connectedly. 

In  the  beginning  of  the  year  1802  I  was  recalled  to 
Bavaria.  I  was,  therefore,  obliged  to  leave  London  in 
the  early  part  of  the  month  of  May,  after  I  had  actually 
begun  on  a  very  few  only  of  the  experiments  which 
I  had  planned  with  so  much  pains.  But  as  I  was 
firmly  resolved  to  devote  myself  to  them  again,  as  soon 
as  I  could  obtain  any  leisure,  however  little,  I  took 
back  to  Germany  with  me  the  greater  part  of  this  ap- 
paratus which  I  had  procured  during  my  stay  in  Eng- 
land. 

During  my  journey,  I  remained  three  months  at 
Paris,  so  that  I  did  not  reach  Munich  before  the  end 
of  August.  In  the  early  part  of  the  month  of  October, 
however,  I  began  my  experiments. 

As  I  had  not  been  able  to  bring  with  me  from  Lon- 
don the  four  large  reflectors  belonging  to  the  Royal 
Institution,  and  as  I  could  not  procure  similar  ones 
in  Bavaria,  I  was  obliged  to  change  the  plan  of  my 
investigations,  and  to  try  whether  it  might  not  be  pos- 
sible to  discover  the  radiation  from  bodies  in  some 
other  way,  and  to  make  the  effects  of  these  radiations 
manifest  without  the  aid  of  the  concentration  brought 
about  by  means  of  the  metallic  reflectors. 

In  the  first  experiments  which  I  undertook,  I  had 
this  object  in  view,  to  determine  whether  the  invisible 
heating  rays  which  a  warm  body  (a  heated  stove,  for 
example)  gives  out  are  not  of  the  same  character  as 
those  coming  from  the  sun.  For  this  purpose  I  pro- 
cured three  cylindrical  boxes  of  very  thin,  soft  wood, 

VOL.  ii.  15 


226  Historical  Review  of  Experiments 

precisely  alike,  four  and  a  half  inches  in  diameter,  three 
inches  high,  and  open  above.  In  each  of  these  boxes, 
an  inch  and  a  quarter  from  the  bottom,  I  put  a  cir- 
cular metallic  disk,  a  quarter  of  a  line  in  thickness,  and 
of  the  same  diameter  as  the  inside  of  the  box.  This 
disk,  which  formed  a  sort  of  optical  screen  in  the  in- 
side of  the  box,  was  fastened  in  its  place  by  a  number 
of  very  short  wooden  pegs,  which  went  through  the  side 
of  the  box. 

In  the  middle  of  the  bottom  of  the  box  was  a  circular 
aperture,  three  quarters  of  an  inch  in  diameter,  closed 
by  a  cork  stopper. 

In  this  stopper  was  a  hole  of  three  lines'  diameter, 
into  which  fitted  a  small  mercurial  thermometer  pro- 
vided with  an  oval  reservoir.  The  divisions  of  the 
scale  were  engraved  upon  the  tube  itself.*  By  means 
of  this  stopper  the  thermometer  was  introduced  into 
the  inside  of  the  box  in  such  a  way  that  its  bulb  was 
situated  in  the  axis  of  the  box,  and  in  the  middle  of 
the  space  between  the  bottom  and  the  metallic  disk. 
This  space,  which  was  designed  to  serve  as  a  reser- 
voir of  heat,  was  filled  with  a  certain  quantity  of  flat 
silver  threads,  which  had  been  picked  out  of  old  silver 
lace. 

In  one  box  the  metallic  disk  or  reflector  was  brass; 
in  the  second,  tinned  iron  ;  and  in  the  third,  ordinary 
sheet-iron. 

*  I  had  four  such  thermometers  made  for  me  in  England,  and  they  did  me  good 
service  throughout  the  whole  course  of  my  experiments  on  the  subject  of  heat.  Their 
tubes  were  made  of  very  hard  glass,  three  lines  in  diameter,  and  were  polished  down 
on  one  side  so  as  to  present  a  flat  surface,  on  which  the  divisions  of  the  scale  were 
etched  with  fluoric  acid.  The  tubes  are  six  or  seven  inches  long,  and  the  bulbs  for  the 
mercury  are  pear-shaped,  and  consequently  not  so  liable  to  get  broken  as  cylindrical 
ones.  In  the  pointed  or  lower  part  of  the  pear,  the  glass  can  be  quite  thick  without 
any  disadvantage. 


on  the  Subject  of  Heat. 


227 


The  accompanying  figure  represents  the  vertical  sec- 
tion of  one  of  these  boxes  in  a  horizontal  position. 
The  stopper  is  also  shown  by  diagonal  lines,  and  a  part 
of  the  thermometer  in  its  proper  place. 


In  order  to  diminish  the  loss  of  heat  which  might 
take  place  through  the  bottom  and  the  sides  of  the  box, 
each  one  was  covered  inside  and  outside  with  well-sized 
paper,  then  coated  three  times  with  copal  varnish,  and, 
in  addition  to  this,  they  were  covered  during  the  experi- 
ment with  an  envelope  of  fur. 

When  one  of  the  boxes  was  placed  for  a  certain 
length  of  time  in  the  sun,  so  that  its  rays  fell  vertically 
upon  the  metallic  disk,  there  was  a  certain  amount  of 
heat  excited  in  the  same  ;  and,  as  this  heat  was  evenly 
distributed  within  the  box  by  means  of  the  metallic 
threads,  it  was  possible  to  observe  very  exactly  the  vari- 
ous degrees  of  heat  by  means  of  the  thermometer ;  if 
all  three  boxes  were  placed  at  the  same  time  in  the  sun, 
it  was  possible  to  determine  with  certainty  the  relative 
amounts  of  heat  excited  at  the  surface  of  the  three  differ- 
ent metals  used  in  the  experiment. 


228  Historical  Review  of  Experiments 

I  was  not  at  all  surprised  to  find  that  the  rays  of  the 
sun  excited  more  heat  in  a  given  time  on  the  black  and 
unpolished  iron  disk  than  on  the  other  two  disks,  which 
were  bright  and  polished ;  I  was,  however,  all  the  more 
astonished  by  an  entirely  unexpected  circumstance  which 
I  noticed  by  chance  during  the  cooling  of  the  instru- 
ments which  had  just  been  heated  by  the  sun,  a  cir- 
cumstance which  arrested  my  attention. 

After  I  had  placed  the  three  boxes  close  together,  and 
had  exposed  them  to  the  influence  of  the  sun's  rays 
until  each  had  reached  its  maximum  temperature,  1 
took  them  away  from  the  window  at  which  they  had 
been  standing  at  the  time,  and  put  them,  bottom  up- 
wards, on  a  cold  table  in  a  corner  of  the  room. 

As  I  happened,  about  a  quarter  of  an  hour  later,  to 
go  past  the  table,  I  cast  a  single  glance  at  the  ther- 
mometers, which  now,  in  a  vertical  position,  projected 
from  the  reversed  boxes.  To  my  no  slight  astonish- 
ment, I  saw  that  the  box  which  before  contained  the 
most  heat  (the  one  which  had  the  iron  disk)  was  now 
the  coldest  of  all. 

This  phenomenon  surprised  me  so  much  the  more, 
as  I  was  convinced  that  this  rapid  cooling  could  not  be 
due  to  the  fact  that  this  box  did  not  have  sufficient 
room  to  take  up  just  as  much  heat  as  the  others.  For, 
as  I  very  well  knew  how  much  in  these  experiments 
depended  upon  the  boxes  being  precisely  alike  as  regards 
their  contents,  I  had  taken  the  greatest  pains  by  similar 
distribution  of  the  silver  threads  to  arrange  them  alike 
before  I  began  my  experiments. 

I  cannot  allow  myself  here  to  give  in  detail  all  the 
conjectures  and.  projected  experiments  of  which  this  dis- 
covery was  the  cause.  I  will,  therefore,  say  nothing 


on  the  Subject  of  Heat.  229 

further  except  that  it  made  a  firm  and  lasting  impression 
on  my  mind,  and  afterwards  exerted  much  influence  on 
the  manner  in  which  I  carried  on  my  inquiries. 

Meanwhile  I  did  not  allow  this  occurrence  to  hinder 
me  in  the  least  from  carrying  out  to  the  end  the  experi- 
ments for  which  I  had  devised  my  apparatus.  I  had, 
therefore,  a  cylindrical  iron  stove  put  into  the  middle 
of  a  large  room,  and  having  surrounded  it  with  fire- 
screens, I  caused  all  the  windows  in  the  room  to  be 
opened.  When  the  stove  was  sufficiently  heated,  I 
found  that  no  sensible  change  had  taken  place  in  the 
mean  temperature  of  the  room.  I  now  removed  the 
screens  which  surrounded  the  stove,  and  placed  all  three 
of  the  boxes  at  the  same  time  in  the  same  position,  that 
is,  twenty-four  inches  from  the  stove. 

The  box  containing  the  iron  disk,  which  previously 
had  contained  the  most  heat  after  standing  in  the  rays 
of  the  sun,  was  also  now  the  warmest  after  being  sub- 
jected to  the  influence  of  the  rays  which  proceeded, 
although  invisibly,  from  the  stove. 

In  order  to  become  more  closely  acquainted  with 
these  rays,  I  had  several  new  instruments  constructed ; 
among  others,  four  large  air  thermometers,  and  three 
other  thermometers  of  the  same  size  filled  with  spirit 
of  wine.  The  bulbs  of  these  thermometers  were  an 
inch  and  three  quarters  in  diameter,  and  contained  either 
various  substances  mixed  with  air  or  else  simply  spirit 
of  wine.  The  bulb  of  the  first  thermometer  was  filled 
with  air  alone;  in  the  second  was  a  mixture  of  air  and 
eider-down  ;  in  the  third  a  mixture  of  air  and  very 
thin  flat  silver  threads ;  the  fourth  contained  air,  eider- 
down, and,  at  the  same  time,  flat  silver  threads. 

In  the  bulb  of  the  first  of  the  thermometers  filled 


230  Historical  Review  of  Experiments 

with  spirit  of  wine,  there  was  nothing  besides  this 
fluid,  in  the  second  there  was  a  mixture  of  spirit  of 
wine  and  eider-down,  and  in  the  bulb  of  the  third  ther- 
mometer there  was  a  mixture  of  spirit  of  wine  and  flat- 
tened silver  threads. 

If,  then,  I  exposed  these  thermometers  in  turn,  now 
to  the  influence  of  the  rays  of  the  sun,  and  again  to  the 
influence  of  rays  coming  from  bodies  warmed  by  the 
fire,  I  could,  from  the  rapid  or  gradual  heating  of  the 
different  thermometers,  arrive  at  a  sufficiently  just  con- 
clusion with  regard  to  the  identity  of  the  radiations  or 
to  the  difference  between  them. 

It  would  be  too  tedious  if  I  were  to  describe  these 
experiments  here  in  detail.  From  some  of  them  I 
obtained  many,  in  certain  respects,  very  remarkable 
results,*  which  allowed  me  to  draw  such  conclusions  as 
pointed  out  clearly  enough  the  way  in  which  I  must 
proceed  towards  the  chief  object  of  my  researches. 

I  afterwards  procured  other  thermometers  of  very 
large  size.  Their  bulbs  are  round,  and  are  made  of 
copper ;  they  are  four  inches  in  diameter.  Their  tubes, 
which  are  glass,  are  thirty  inches  long,  and  are  filled 
with  linseed  oil.  I  use  them  in  experiments  designed 
to  determine  the  relative  rapidity  with  which  a  warm 
body  (the  thermometer  itself)  cools  in  different  liquids 
having  the  same  temperature.  This  instrument  is  the 

*  I  noticed,  among  other  things,  that  the  thermometer  whose  bulb  contained  a 
mixture  of  spirit  of  wine  and  flat  silver  threads  was  much  more  sensitive  in  general, 
and  especially  to  very  slight  changes  of  temperature,  than  another  thermometer  of  the 
same  size,  the  bulb  of  which  contained  only  spirit  of  wine.  It  would,  perhaps,  be  of 
advantage  to  procure  similar  thermometers  to  use,  if  not  ordinarily,  at  least  on  certain 
occasions.  I  am  firmly  convinced  that  a  thermometer  whose  bulb  is  filled  with 
mercury  and  platina  cut  into  threads  will  be  much  more  sensitive,  that  is,  will  indicate 
the  temperature  much  more  quickly,  than  a  thermometer  of  the  same  size  filled,  as  is 
usual,  with  mercury  alone. 


on  the  Subject  of  Heat.  231 

only  one  that  I  could  ever  devise  for  such  experiments 
without  fearing  important  objections  on  account  of  the 
apparatus  employed. 

I  possess,  also,  various  other  thermometers,  intended 
simply  to  receive  and  collect  within  themselves  the  calo- 
rific or  frigorific  rays  which  fall  upon  their  surfaces. 
The  reservoir  of  each  consists  of  two  cones  of  very  thin 
sheet  brass,  which  lie  one  within  the  other,  and  are 
fastened  to  each  other,  on  the  under  side,  in  such  a  way 
that  there  is  an  empty  space,  not  quite  a  line  in  width, 
between  the  inner  surface  of  the  outer  cone  and  the 
outer  surface  of  the  inner  cone.  The  inner  cone  is  four 
inches  in  diameter,  four  inches  high,  and  ends  in  a 
point  above.  The  diameter  of  the  oufer  cone  is  four 
and  a  quarter  inches,  and  it  ends  above  in  a  cylindrical 
tube  three  quarters  of  an  inch  in  diameter  and  four 
inches  long.  In  this  cylinder  is  fixed  a  glass  ther- 
mometer tube,  and  if  the  space  between  the  two  cones 
be  filled  with  linseed  oil  or  coloured  spirit  of  wine,  this 
instrument  answers  the  same  purpose  as  an  ordinary 
thermometer.  The  scale  of  this  thermometer  is  fastened 
firmly  to  this  glass  tube. 

The  outer  wall  of  the  instrument  is  shielded  and 
protected  from  the  calorific  or  frigorific  influences  of 
the  surrounding  air  by  means  of  a  cylindrical  box  of 
dry  wood,  thickly  coated  with  varnish,  and  filled  with 
eider-down  ;  into  this  the  body  of  the  instrument  fits. 
This  cover  is  four  and  a  half  inches  high,  and  is,  on  the 
inside,  of  the  same  diameter  as  the  lower  part  of  the 
outer  cone ;  and  the  tube  of  the  instrument,  with  its 
attached  scale,  goes  through  a  hole  made  in  the  bottom 
of  the  box. 

If,    now,   the  outer   blackened    surface  of  the  inner 


232  Historical  Review  of  Experiments 

cone  be  held  in  the  neighbourhood  of  and  towards  an 
object  which  is  giving  off  calorific  (or  frigorific)  rays, 
the  heat  (or  cold)  caused  by  these  rays  is  communicated 
to  the  fluid  contained  in  the  space  between  the  two 
cones,  and  this  change  of  temperature  brings  about  a 
corresponding  change  in  the  level  of  the  liquid  in  the 
upper  part  of  the  tube ;  by  this  means  the  amount  of 
heat  (or  cold)  communicated  can  be  estimated  and 
measured. 

An  instrument  of  this  description,  which  I  procured 
in  the  year  1801,  during  my  stay  in  England,  is  at 
present  in  the  physical  cabinet  of  the  Royal  Institu- 
tion at  London.  Two  similar  ones,  fitted  up  in  Bava- 
ria, are  still  kept  in  my  cabinet  at  Munich.  I  have 
described  this  instrument  thus  minutely,  simply  because 
I  am  convinced  that  it  is  of  very  great  service  in  ex- 
periments on  the  calorific  and  frigorific  radiations  from 
various  bodies,  and  because  it  has  been  my  earnest  de- 
sire to  induce  natural  philosophers  to  devote  their  atten- 
tion to  this  subject,  so  worthy  of  investigation. 

It  only  remains  for  me  to  say  a  few  words  in  regard 
to  the  experiments  which  I  have  described  very  fully 
in  the  memoir  read  before  the  Royal  Society  on  the 
^d  of  February,  1804,  which  has  been  translated  into 
French  by  Professor  Pictet.* 

I  performed  these  experiments  in  Munich,  in  1803, 
during  the  months  of  January,  February,  and  March. 
According  as  the  results  seemed  of  importance,  I  imme- 
diately acquainted  my  friends  in  England  and  France 
with  -them.  Among  others,  I  communicated  to  Sir 
Joseph  Banks,  then  President  of  the  Royal  Society  of 
London,  the  very  striking  results  of  an  experiment 

*  See  page  23. 


on  the  Subject  of  Heat.  233 

which  I  made,  on  the  nth  of  March,  with  two  metal- 
lic vessels,  both  of  which  —  one  being  naked,  and  the 
other  having  a  covering  of  linen  —  I  allowed  to  cool, 
exposed  to  the  air,  after  having  first  filled  them  with 
warm  water.  In  addition  to  this,  I  wrote  him  that 
I  had  made  several  experiments  with  various  vessels 
blackened  and  covered  with  repeated  coatings  of  varnish, 
and  I  announced  the  results  obtained.  I  also  informed 
him  of  the  discovery  which  I  made,  with  the  help  of  my 
tkermoscope,  that  different  bodies  of  the  same  tempera- 
ture give  out  very  different  quantities  of  calorific  rays, 
and  that  frigorific  rays  have  just  as  real  an  existence  as 
the  calorific  rays  from  warm  bodies. 

Since  Sir  Joseph  showed  my  letters  to  various  per- 
sons, and  since  I  did  not  keep  my  experiments  or  their 
results  a  secret  from  him  or  from  any  one  else,  my  dis- 
covery was  publicly  mentioned  in  London  even  as  early 
as  the  spring  of  the  past  year.  As  an  incontrovertible 
proof  of  this  fact,  I  can  bring  forward  a  letter  from  a 
friend  of  mine  (to  whom  I  had  not  mentioned  my  new 
discovery  in  any  way),  in  which  he  congratulates  me 
on  the  success  of  my  researches,  and  informed  me  at 
the  same  time  that  he  had  learned  what  he  knew  with 
regard  to  my  discoveries  from  Mr.  Davy,  a  Professor 
in  the  Royal  Institution,  who  had  spoken  publicly  of 
them  in  his  lectures  on  chemistry. 

The  memoir  in  which  I  gave  an  account  of  my  in- 
vestigations was  finished  early  in  May  (1803);  m  the 
early  part  of  June  I  left  Munich  for  a  journey  into 
Switzerland.  As  I  intended  to  proceed  from  Geneva  to 
Paris,  I  took  with  me  my  memoir  and  some  of  my 
newly  invented  instruments,  and  among  others  the  ther- 
moscope. 


234  Historical  Review  of  Experiments 

On  reaching  Geneva,  in  August,  I  read  my  memoir 
in  the  presence  of  Professor  Pictet,  De  Saussure,  and 
various  other  persons,  and  at  the  same  time  repeated 
some  of  my  experiments  with  the  thermosc'ope. 

As  soon  as  I  reached  Paris,  in  the  latter  part  of  Oc- 
tober, I  had  my  memoir  copied  (by  Mr.  Cadel,  of  Glas- 
gow, who  was  then  in  Paris),  and  sent  it,  in  the  middle 
of  December,  to  London  by  the  younger  Mr.  Living- 
ston, who  was  kind  enough  to  deliver  it  in  person  to 
Sir  Joseph  Banks  on  the  2jd  of  December.  As  the 
Christmas  recess  of  the  Royal  Society  begins  just  after 
this  time,  my  memoir  could  not  be  read  in  a  public 
meeting  of  the  Society  until  the  3d  of  February. 

The  6th  of  June  there  were  sent  to  me  from  Lon- 
don (through  the  elder  Mr.  Livingston,  Minister  Pleni- 
potentiary of  the  United  States  of  North  America  at 
Paris)  two  copies  of  my  memoir,  published  by  order 
of  the  Royal  Society.  At  the  same  time  I  received  a 
letter  from  Mr.  Davy,  Professor  of  Chemistry  at  the 
Royal  Institution,  in  which  he  informed  me  that  Mr. 
Leslie  had,  a  short  time  previously,  published  a  me- 
moir on  heat,  and  that  in  it  he  had  described  various 
experiments  which  bore  a  resemblance  to  some  which  I 
had  performed. 

The  id  of  June  I  received  at  Paris,  from  M.  Ber- 
tholet,  Mr.  Leslie's  book,  which  was  sent  to  me  by 
Sir  Joseph  Banks.  M.  Bertholet  had  at  the  same  time 
received  from  England  a  copy  of  the  work,  which  was 
sent  to  him  by  one  of  his  friends  there. 

As  I  had,  only  a  short  time  before,  occupied  the 
attention  of  the  National  Institute  with  an  account 
of  my  recent  researches  and  discoveries,*  the  appear- 

*  Between  the  igth  of  March  and  the  yth  of  May,  1804,  I  presented  to  the  Na- 


on  the  Subject  of  HeaL  235 

ance  of  a  book  coming  from  England,  and  containing 
a  description  of  a  number  of  experiments  and  discov- 
eries in  many  respects  not  dissimilar  to  my  own,  could 
not  fail  to  create  a  certain  feeling  of  surprise  among  the 
philosophers  of  Paris,  as  I  could  plainly  enough  per- 
ceive. I  find  myself,  therefore,  compelled,  although 
against  my  will,  to  explain  as  far  as  possible  an  occur- 
rence which  it  is  highly  important  for  me  should  appear 
in  its  true  light. 

I  am  far  from  intending  to  assert  that  Mr.  Leslie  had 
any  knowledge  of  those  experiments  of  mine  which 
bore  a  resemblance  to  those  which  he  announced  pub- 
licly in  print.  It  is,  however,  equally  certain  that  I 
did  not  know,  and  could  not  have  known,  the  least 
thing  about  his.  It  will  not  be  difficult  for  me  to  prove 
this. 

It  might,  perhaps,  be  just  as  easy  for  Mr.  Leslie  to 
bring  forward  proofs  that  he  knew  absolutely  nothing 
about  my  experiments.  This  would  be  all  the  more 
readily  believed  as  he  (in  the  course  of  certain  remarks 
made  in  a  note  with  regard  to  the  observations  which 
I  offered  in  explanation  of  the  propagation  of  heat  in 
liquids)  speaks  of  me  as  of  a  man  already  dead*  at  the 
time  when  he  made  these  remarks. 

It  is  certain  that  we  are  perfect  strangers  to  each 
other,  that  we  do  not  know  each  other  even  by  sight, 
and  that  we  never  had  any  sort  of  correspondence  with 
each  other. 

As  regards  the  priority  of  the  public  announcement  of 
our  discoveries,  this  point  can  be  easily  made  clear  by 

tional  Institute  five  different  memoirs  on(this  subject.  They  will  probably  be  printed 
in  the  "  Memoires  de  1'Institut." 

*  See  the  thirty-ninth  note  at  the  end  of  his  work,  beginning  with  the  following 
words  :   ^  A  late  ingenious  experimenter." 


236  Historical  Review  of  Experiments 

the  statement  of  certain  facts  which  do  not  admit  of 
doubt. 

It  is  true  that  I  cannot  determine  with  any  great  ac- 
curacy the  time  when  Mr.  Leslie's  book,  first  saw  the 
light ;  it  cannot,  however,  possibly  have  been  published 
before  the  middle  of  May  of  this  year,  for  the  dedica- 
tion is  dated  at  Largo,  in  Fifeshire  (Scotland),  the  2oth 
of  May,  1804.  This  would  be,  consequently,  nearly  a 
year  after  the  time  when  the  most  remarkable  results 
of  my  investigations  were  known  in  London  ;  it  would 
be  nine  months  from  the  time  when,  in  Geneva,  I  read 
the  memoir  containing  the  circumstantial  and  detailed 
account  of  these  investigations  in  the  presence  of  a 
number  of  celebrated  philosophers  ;  it  would  be  five 
months  later  than  the  time  at  which  this  memoir  was 
placed  in  the  hands  of  the  President  of  the  Royal  So- 
ciety of  London  ;  and  it  would  be  more  than  a  quarter 
of  a  year  from  the  time  at  which  it  was  read  publicly 
before  this  Society. 

Still  the  •priority  in  question,  considered  in  and  by 
itself,  is  of  such  slight  importance  that  I  should  not 
have  mentioned  it  at  all,  were  it  not  that  the  facts  which 
go  to  establish  it  tend  at  the  same  time  to  strengthen  a 
far  more  important  assertion,  namely,  that  I  am  actually 
the  discoverer  of  what  I  announced  as  discoveries. 

If  Mr.  Leslie  and  myself,  the  one  in  Scotland,  the 
other  in  Bavaria,  each  for  himself  and  at  about  the 
same  time,  did  actually  make  the  same  discoveries,  this 
is  a  condition  of  things  which  has  already  happened 
more  than  once  before  our  time ;  and  then,  as  far  as  the 
interpretation  of  these  phenomena  is  concerned,  we  dif- 
fer from  each  other  in  our  mode  of  explanation  to  such 
an  extent  that  there  can  no  question  arise  between  us 


on  the  Subject  of  Heat.  237 

in  regard  to  the  ownership  of  our  opinions.  Nothing 
is  more  certain  than  that,  in  this  respect,  we  have  not 
borrowed  one  from  the  other  in  the  slightest  degree. 

Besides,  I  have  every  reason  for  believing  that  even 
if  I  had  not  described  so  particularly  the  facts  which  I 
have  brought  forward,  still  all  those  who  will  take  the 
trouble  to  consider  impartially  the  numerous  experi- 
ments on  the  subject  of  heat  which  I  have  made  dur- 
ing more  than  twenty  years,  will  be  convinced  that  I 
must  have  been  led  to  the  investigations  and  discoveries 
in  question  by  the  entirely  natural  connection  of  ideas 
caused  by  my  opinions  on  the  subject,  without  needing 
to  borrow,  in  the  slightest  degree,  from  any  person 
whomsoever. 

To  close  this  historical  review  of  my  various  re- 
searches on  the  subject  of  heat,  I  will  give  a  very  brief 
account  of  my  labours  in  this  connection,  from  my 
arrival  in  Paris,  until  the  close  of  the  month  of  October 
of  the  last  year  (1803). 

As  I  had  brought  with  me  two  thermoscopes,  I  had 
them  adjusted,  by  Dumontier,  with  all  possible  care;  I 
also  sent  to  Munich  for  several  other  instruments  which 
I  had  used,  the  year  before,  in  my  experiments  on 
heat. 

I  also  procured  several  new  instruments,  in  order  to 
make  new  experiments  ;  among  others,  an  apparatus 
which  I  intended  to  use  to  determine  the  progress  of 
heat  in  a  massive  bar  of  metal,  in  glass,  and  in  other 
solid  substances.  All  these  instruments  I  showed  to 
several  members  of  the  National  Institute,  namely,  to 
MM.  Laplace,  Delambre,  Prony,  and  Biot. 

To  these  philosophers,  and  at  the  same  time  to  M. 
Bertholet  as  well,  I  proposed  to  perform  the  now  well- 


238  Historical  Review  of  Experiments 

known  experiment  of  the  cold  body  and  the  speaking- 
tube  (and  this  was  before  the  instrument  necessary  for 
the  purpose  had  been  invented),  and  thus  to  terminate 
our  (in  all  respects  very  friendly)  controversy  on  the 
reality  of  caloric. 

This  experiment  was  afterwards  performed  in  the 
physical  cabinet  of  the  National  Institute  in  the  pres- 
ence of  Laplace,  Bertholet,  and  Charles.  The  result 
was  precisely  as  I  had  predicted. 

On  the  28th  Ventose  of  the  year  12  (the  I9th  of 
March,  1804)  I  presented  to  the  Mathematical  and 
Physical  Class  of  the  National  Institute  my  first  me- 
moir, in  which  I  described  my  thermoscope  and  a  few 
of  the  discoveries  that  I  had  made  with  the  help  of 
this  instrument. 

On  the  fth  Germinal  (26th  of  March,  1804)  I  pre- 
sented to  the  same  Class  a  second  memoir,  in  which  I 
sought  to  develop  my  ideas  on  the  nature  of  heat,  as 
well  as  on  the  manner  in  which  it  is  excited  and  com- 
municated. At  the  same  time  I  gave  the  results  of  cer- 
tain experiments  which  I  had  made  on  the  cooling  of 
warm  bodies  in  the  air.  . 

On  the  i  gth  Germinal  (pth  of  April,  1804)  I  pre- 
sented to  the  Class  a  third  memoir,  which  treated  of  an 
experiment,  which  I  had  recently  made  in  Paris,  on  the 
nature  of  heat ;  by  this  experiment  the  influence  of  the 
rays  emanating  from  cooling  bodies  was  rendered  mani- 
fest in  a  manner  entirely  new. 

On  the  loth  Floreal  (joth  of  April,  1804)  my  fourth 
memoir  was  presented  to  the  Class.  In  this  memoir  I 
described  an  experiment  which  I  performed  with  two 
flasks  of  equal  size.  One  was  made  of  glass,  the  other 
of  tinned  iron.  Both  were  filled  with  boiling  water, 


on  tJie  Subject  of  Heat.  239 

and  exposed  at  the  same  time  to  the  air,  in  which  they 
were  allowed  to  cool.  The  water  contained  in  the  glass 
flask  cooled  twice  as  fast  as  that  in  the  one  made  of 
tinned  iron,  although  the  walls  of  the  latter  were  much 
thinner  than  those  of  the  glass  flask.  This  memoir 
ends  with  some  considerations  on  the  comparison  which 
has  been  instituted  between  a  warm  body  and  a  sponge 
filled  with  water,  and  on  the  influence  of  radiation  dur- 
ing the  warming  and  cooling  of  bodies. 

On  the  iyth  Floreal  (yth  of  May,  1804)  I  laid  before 
the  Class  my  fifth  memoir,  in  which  I  gave  an  account  of 
an  entirely  new  series  of  experiments,  which  I  had  made 
in  Paris,  on  the  manner  in  which  heat  is  propagated  in 
a  massive  bar  of  metal,  six  inches  long  ana  an  inch  and 
a  half  in  diameter.  This  bar  was  heated  at  one  end 
by  boiling  water,  and  cooled  at  the  other  end  some- 
times with  a  mixture  of  pounded  ice  and  water,  and 
sometimes  simply  with  water  of  the  temperature  of  the 
air. 

M.  Biot,  member  of  the  Institute,  made,  at  about  the 
same  time  with  myself,  several  successive  experiments 
on  the  propagation  of  heat  in  metallic  bars  and  other 
solid  bodies.  He,  however,  used  for  this  purpose  bars 
of  a  different  length  from  mine,  and  higher  tempera- 
tures. Otherwise  we  obtained  the  same  results  from 
our  experiments. 

He  hit  upon  the  fortunate  idea  of  employing  similar 
experiments  for  measuring  very  high  degrees  of  tem- 
perature ;  such,  for  example,  as  is  necessary  in  the 
preparation  of  porcelain,  or  for  melting  metals  not 
readily  fusible. 

As  I  was  invited  to  prepare  a  condensed  description 
of  my  recent  experiments  on  heat,  to  be  read  at  the 


240   Historical  Review  of  Experiments  on  Heat. 

public  sitting  of  the  National  Institute  on  the  6th 
Messidor  (June  26,  1804),  I  presented  the  memoir 
which  follows.*  As  it  has  already  been  printed  (in 
the  Moniteur  of  the  pth  Messidor,  or  the  29th  of  June, 
1804),  I  may  be  allowed  to  introduce  it  into  this  col- 
lection. The  case  is  otherwise  with  the  five  other  me- 
moirs which  I  presented  to  the  first  class  of  the  Insti- 
tute; for  as  they  will  be  embodied  in  the  Me'moires 
of  the  Class  it  would  not  be  proper  for  me  to  publish 
them  earlier. 

To  complete  this  historical  review,  I  must,  in  addi- 
tion, say  a  word  or  two  on  my  attempts  to  perfect  the 
application  of  heat  to  the  arts  and  to  all  sorts  of  domes- 
tic purposes.  Among  the  fifteen  Essays  which  I  have 
published  in  three  octavo  volumes  are  no  less  than 
eight  which  treat  of  the  use  of  heat.  They  are  as  fol- 
lows :  — 

Essay  IV.  Of  Chimney  Fireplaces ;  VI.  On  the 
Management  of  Fire  and  Economy  of  Fuel ;  X.  Of 
Kitchen  Fireplaces;  XII.  Of  the  Salubrity  of  Warm 
Rooms  in  Winter;  XI II.  Of  the  Salubrity  of  Warm 
Baths,  and  the  Mode  of  their  Preparation  ;  XIV.  Of 
the  Management  of  Fire  in  Closed  Fireplaces  ;  XV. 
Of  the  Use  of  Steam  as  a  Vehicle  for  transporting 
Heat. 

*  See  page  166. 

[This  paper  is  translated  from  the  German,  as  it  appears  in  Vol.  IV. 
of  Rumford's  Kleine  Schriften.] 


EXPERIMENTS   AND    OBSERVATIONS 


COOLING    OF    LIQUIDS    IN   VESSELS    OF    PORCELAIN, 
GILDED   AND   NOT   GILDED. 

NOTHING  affords  more  entertainment  than  to 
compare  the  processes  of  the  common  arts  of 
life  and  the  ordinary  habits  of  the  people  in  their 
household  operations  with  the  principles  of  the  physi- 
cal and  mathematical  sciences.  This  comparison  often 
presents  very  curious  points  of  resemblance,  and  leads 
sometimes  to  very  important  improvements. 

In  all  countries  where  the  daily  use  of  tea  has  become 
common  among  the  rich,  teapots  of  silver  are  preferred 
to  those  of  porcelain  or  earthenware,  and  the  reason 
given  for  this  preference  is  that  the  beverage  when  pre- 
pared in  the  former  is  of  a  better  quality  than  when  pre- 
pared in  the  latter.  I  was,  for  a  long  time,  of  the 
opinion  that  this  idea  was  owing  simply  to  prejudice, 
and  without  foundation  ;  but,  having  discovered  some 
years  since  that  metallic  vessels,  when  clean  and  bright 
on  the  outside,  possess  the  property  of  causing  warm 
liquids  which  are  put  into  them  to  retain  their  heat  for 
a  very  long  time,  I  began  to  see  that  the  preference  in 
question  might  be  the  legitimate  result  of  long  experi- 
ence, as  is  almost  always  the  case  with  those  preferences 
which  in  the  end  are  universally  adopted. 

VOL.    II.  l6 


242  On  the  Cooling  of  Liquids  in  Vessels 

In  order  to  throw  light  on  this  subject,  which  had  sev- 
eral points  of  interest  for  me,  I  made  the  following- 
experiment.  I  procured  (from  M.  Nast,  a  celebrated 
porcelain  manufacturer,  of  Paris)  two  vessels  of  porce- 
lain, of  the  same  shape  and  of  the  same  dimensions, 
the  one  white,  the  other  completely  covered  on  the  out- 
side with  gilding ;  into  these  vessels  I  put  equal  quan- 
tities (250  grammes,  or  a  quarter  of  a  litre)  of  warm 
water,  and  then  allowed  them  to  cool  gradually  in  a 
large  room  free  from  currents  of  air,  having  placed  them 
three  feet  apart  on  a  table  in  the  middle  of  the  room. 

Each  of  the  vessels  was  closed  with  a  cork  stopper, 
and  by  means  of  a  mercurial  thermometer  with  a  cylin- 
drical bulb,  fixed  in  the  axis  of  the  vessel  in  such  a  way 
that  while  the  thermometer  was  inserted  in  the  cork  the 
scale  remained  on  the  outside  of  the  vessel,  I  noted 
very  conveniently  the  progress  of  the  cooling  without 
touching  the  vessel,  and  without  even  approaching  it 
sufficiently  near  for  the  heat  of  my  body  to  interfere 
sensibly  with  the  operation  of  cooling. 

The  result  of  this  experiment  was  as  I  had  expected. 
The  gilded  vessel  cooled  much  more  slowly  than  the 
plain  one.  Starting  at  the  same  time  with  both  vessels 
at  the  same  temperature,  if  it  took  half  an  hour  for  the 
plain  vessel  to  cool  down  through  a  certain  number  of 
degrees,  three  quarters  of  an  hour  were  necessary  for  the 
gilded  one  to  cool  down  to  the  same  point. 

This  comparative  experiment  was  repeated  several 
times,  and  invariably  with  the  same  result;  the  gilded 
vessel  always  cooled  more  slowly  than  the  plain  one  in 
about  the  proportion  of  3  to  2. 

The  advantage  that  can  be  gained  from  this  remarka- 
ble property,  possessed  by  metallic  surfaces,  of  resisting 


of  Porcelain,  Gilded  and  not  Gilded.          243 

the  cooling  (or  heating)  action  of  surrounding  bodies, 
is  too  evident  to  need  much  explanation.  Since,  in 
household  economy,  use  is  often  made  of  porcelain  ves- 
sels for  holding  warm  liquids,  which  it  is  desired  to 
keep  warm  for  a  long  time,  —  as,  for  example,  tea, 
coffee,  etc.,  —  in  all  such  cases  it  would  be  of  advantage 
to  use  vessels  gilded  on  the  outside ;  or,  if  gilding  be 
found  too  expensive,  it  is  possible  to  use,  and  with 
equal  advantage  as  regards  retaining  the  heat,  vessels 
which  are  silvered  or  covered  with  a  layer,  no  matter 
how  thin,  of  any  other  metal  not  liable  to  be  readily 
oxidized  in  the  air. 

As  to  gilding  the  vessels  on  the  inside,  it  would  be 
to  no  purpose,  for  it  would  add  nothing  to  the  effect  in 
question,  as  I  have  learned  from  the  results  of  several 
experiments.  This,  however,  applies  only  to  simple 
vessels ;  for  in  case  a  double  vessel  were  employed  in 
order  to  retain  more  effectually  the  heat  of  any  sub- 
stance, the  outside  vessel  must  be  gilded  on  the  inside 
as  well  as  on  the  outside ;  in  no  case  is  it  necessary  for 
the  inner  vessel  to  be  gilded  on  the  inside. 

If  it  is  a  question  of  preserving  the  low  temperature 
of  liquids  or  other  cold  substances,  such  as  ice-creams, 
etc.,  in  this  case,  also,  vessels  having  externally  a  polished 
metallic  surface  should  be  used ;  for  a  surface  of  this 
description  throws  off  by  reflection  a  large  portion  of 
the  calorific  rays  which  reach  it  from  surrounding 
objects,  and  consequently  the  vessel  grows  warm  very 
slowly. 

Everybody  knows  how  much  time  it  takes  to  bring 
water  to  boiling  in  a  silver  coffee-pot  which  is  clean  and 
bright  on  the  outside,  especially  before  an  open  fire,  or 
on  glowing  coals  which  burn  without  smoke.  It  is, 


244  ®n  MIC  Cooling  of  Liquids  in  Vessels 

however,  very  easy  to  hasten  materially  the  heating  of 
the  liquid  in  this  case ;  all  that  is  necessary  is  to  begin 
by  blackening  the  outside  of  the  coffee-pot  over  the 
flame  of  a  candle  or  of  a  lamp,  or  to  destroy  or  conceal 
in  some  other  way  the  metallic  lustre. 

All  the  facts  which  I  have  just  detailed  are  easily 
explained,  and,  to  my  mind,  satisfactorily,  by  the  theory 
of  heat  developed  in  the  various  memoirs  on  this  sub- 
ject which  I  have  had  the' honour  of  presenting  to  this 
Assembly  at  different  times. 

If  heat  is  nothing  but  a  vibratory  motion  of  the  par- 
ticles of  a  body,  —  a  motion  which  always  exists  in  all 
bodies,  but  which  has  greater  or  less  rapidity  or  inten- 
sity according  to  the  temperature  of  those  bodies,  —  and 
if  a  body  which  is  warmer  than  those  which  surround  it 
is  cooled  on  being  exposed  to  their  influence,  not  because 
it  has  transferred  to  them  something  material,  to  which 
the  name  of  caloric  has  been  given,  but  because  of  the 
effect  of  the  action  upon  it  of  those  bodies  by  means  of 
their  frigorific  rays,  that  is  to  say,  by  the  undulations 
caused  in  the  surrounding  mass  of  the  fluid  ether,  —  un- 
der these  circumstances  it  is  evident  that  the  nature  of 
the  exterior  surface  of  the  warm  body,  which  renders 
it  more  or  less  capable  of  reflecting  the  rays  or  undula- 
tions which  reach  it  from  surrounding  objects  colder 
than  itself,  ought  to  influence  to  a  considerable  extent 
the  rapidity  of  the  cooling  process. 

Now,  we  know  that,  of  all  the  substances  with  which 
we  are  acquainted,  the  metals  are  the  most  impervious 
to  light,  and,  at  the  same  time,  and  perhaps  as  a  neces- 
sary consequence,  have  for  it  the  greatest  reflecting 
power;  moreover,  the  results  of  a  large  number  of 
experiments  have  shown  that  they  also  possess  in  an 


of  Porcelain,  Gilded  and  not  Gilded.          245 

eminent  degree  the  power  of  reflecting  the  invisible  rays 
or  undulations  which  all  objects  in  nature  send  off  con- 
tinually and  in  all  directions  from  their  surfaces  in  con- 
sequence of  that  peculiar  motion  of  their  particles  which 
constitutes  their  temperature. 

Hence  it  appears  that  vessels  having  a  metallic  sur- 
face on  the  outside  must  be  well  adapted  for  preserving 
the  temperature  of  the  substances  which  they  contain, 
whether  that  temperature  be  high  or  low,  warm  or  cold. 

I  am  far  from  maintaining  that  the  sort  of  material 
of  which  the  vessel  is  made,  and  the  thickness  of  its 
walls,  are  matters  entirely  indifferent,  provided  that  the 
outer  surface  be  covered  with  a  thin  metallic  layer  which 
is  clean  and  bright.  I  am  aware  that  neither  heat  nor  cold 
can  be  communicated  or  propagated  through  the  walls 
of  a  vessel,  or  of  any  other  solid  body,  instantaneously, 
and  that  this  communication  takes  place  more  quickly 
in  some  substances  than  in  others,  more  quickly 
through  a  thin  wall  than  through  a  thick  wall  of  the 
same  material ;  and  it  is  evident  that  this  difference 
must  necessarily  exert  an  influence  on  the  rapidity  of 
the  change  of  temperature  of  the  vessel  and  of  the 
liquid  it  contains,  whatever  be  the  nature  of  the  exter- 
nal surface  of  the  vessel. 

For  example,  as  porcelain  is  a  worse  conductor  of 
heat  than  gold  or  silver,  a  vessel  of  given  form  and 
dimensions,  made  of  porcelain  and  well  gilded  on  the 
outside,  if  filled  with  warm  water,  would  cool  rather 
more  slowly  in  the  air,  or  even  in  a  Torricellian  vacuum, 
than  another  vessel  of  the  same  dimensions  made  of 
gold  or  silver,  and  filled  with  water  of  the  same  tem- 
perature ;  but  if  the  vessels  were  exposed  at  the  same 
time  to  a  strong  and  very  cold  current  of  air,  or  were 


246  On  the  Cooling  of  Liquids  in  Vessels 

plunged  into  cold  water,  the  difference  in  the  rate  of 
cooling  would  be  much  greater. 

Hence  we  may  conclude  that  teapots  and  coffee-pots 
made  of  porcelain  or  earthenware  and  well  gilded  on 
the  outside  would  be  not  only  as  good,  but  even  better 
for  common  use  than  teapots  and  coffee-pots  made  of 
silver. 

If  equal  quantities  of  warm  water  are  placed  in  two 
porcelain  vessels  of  the  same  form  and  dimensions,  and 
with  walls  of  the  same  thickness,  the  one  gilded  on  the 
outside,  the  other  plain,  and  these  vessels  are  allowed 
at  the  same  time  to  cool  in  still  air,  the  gilded  vessel  is 
found  to  cool  more  slowly  than  the  plain  one  in  the 
proportion  of  3  to  2,  as  has  already  been  remarked;  but 
if,  instead  of  allowing  the  vessels  to  cool  in  air  which  is 
undisturbed,  they  are  exposed  to  the  action  of  a  strong 
and  cold  current  of  air,  the  difference  in  the  rapidity  of 
cooling  will  be  much  less,  as  6  to  5,  for  example;  and 
if  the  current  of  air  is  very  strong,  and  at  the  same 
time  very  cold,  this  difference  will  be  still  smaller. 

If,  instead  of  exposing  the  vessels  in  the  air,  they  are 
plunged  into  cold  water,  the  difference  in  the  rapidity 
with  which  they  cool  will  be  reduced  to  almost  nothing. 

In  the  cases  last  mentioned  we  can  say  that  the  ex- 
terior surfaces  of  both  vessels,  although  of  different 
natures,  yet,  on  being  exposed  to  so  great  a  degree  of 
cold,  are  cooled  to  such  an  extent  as  to  be  in  a  condition 
to  transmit  the  heat  coming  from  the  interior  of  the 
vessel  as  fast  as  it  can  reach  them  after  making  its  way 
through  the  thickness  of  the  walls,  which  offer  all  the 
while  a  certain  amount  of  resistance  to  its  passage. 

To  use  another  form  of  expression  which  I  regard  as 
more  exact,  and  consequently  more  suitable,  especially 


of  Porcelain,  Gilded  and  not  Gilded.          247 

before  this  illustrious  Assembly,  it  might  be  said  that  in 
the  case  in  question  the  exterior  surfaces  (the  one  of 
white  porcelain,  the  other  of  gold)  of  the  two  vessels 
being  intimately  exposed  to  the  violent  action  of  a  rapid 
succession  of  the  very  cold  particles  of  the  surrounding 
fluid,  became,  both  of  them,  cooled  to  such  an  extent 
that  they  were  reduced  to  about  the  same  temperature 
in  spite  of  the  continual  heating  action  of  the  walls  of 
the  vessels  in  contact  with  them  on  the  opposite  side ; 
and  that,  as  a  consequence,  since  these  surfaces  exercised 
on  the  walls  of  the  vessels  which  they  covered  cooling 
actions  which  were  sensibly  equal,  the  two  vessels  were 
of  necessity  cooled  with  the  same  rapidity. 

I  will  conclude  this  memoir  with  some  observations 
which  may  serve  to  throw  light  on  a  point  in  the  theory 
of  heat  which  is  of  very  great  importance. 

The  great  rapidity  with  which  heat  is  communicated 
from  one  body  to  another,  when  two  bodies  of  different 
temperatures  are  in  contact,  compared  with  the  slowness 
of  communication  which  takes  place  when  the  bodies 
are  separated,  however  little,  one  from  the  other,  has 
had  a  considerable  tendency  to  give  authority  to  the  opin- 
ion quite  generally  adopted  by  chemists,  that  there  are 
two  modes  by  which  heat  can  be  transmitted  from  one 
body  to  another ;  that  is,  at  a  distance,  by  radiant 
caloric^  and,  on  contact,  by  an  actual  transfusion  of  the 
same  substance.  If,  however,  attention  be  paid  to  a 
fact  which  no  one  up  to  this  time  has  called  into  ques- 
tion, the  phenomenon  under  consideration  can,  as  it 
seems  to  me,  be  explained  in  a  perfectly  clear  and  satis- 
factory manner,  without  having  recourse  to  such  an 
extraordinary  supposition  as  that  there  are  two  different 
modes  by  which  heat  is  communicated. 


248  On  the  Cooling  of  Liqiiids  in  Vessels 

It  is  generally  recognized  (I  might  say  that  it  is 
proved)  that  the  intensity  of  the  action  of  calorific  or 
frigorific  rays  is  inversely  proportional  to  the  squares  of 
the  distances  from  the  body  from  which  they  proceed ; 
now,  if  this  relation  is  constant,  since  the  effect  produced 
by  these  rays  in  a  given  time  must  necessarily  be  in  pro- 
portion to  the  intensity  of  their  action,  it  is  evident 
that  at  the  point  of  contact  (if,  indeed,  there  can  be  an 
actual  contact  between  two  bodies)  the  rapidity  of  the 
calorific  action  between  two  particles  of  different  tem- 
peratures, and  which  are  in  contact,  must  be  infinite. 

But  the  time  necessary  to  establish  an  equality  of 
temperature  throughout  the  entire  masses  of  two  bodies 
in  contact,  which  are  of  sensible  size  and  of  different 
temperatures,  will  depend  not  only  on  the  size  of  the 
bodies  and  on  the  extent  of  the  surfaces  by  which  they 
are  in  contact,  but  also,  and  above  all,  on  the  greater  or 
less  rapidity  with  which  is  propagated  among  the  parti- 
cles of  the  bodies  that  peculiar  motion  of  those  particles 
which  constitutes  their  temperature. 

I  will  observe  here,  in  passing,  that  if  in  the  commu- 
nication of  heat  between  two  bodies  in  contact,  it  were 
only  a  question  of  the  transfer  from  one  to  the  other  of 
the  excess  of  a  fluid  as  rare  and  as  elastic  as  caloric  is 
supposed  to  be,  one  would  expect,  it  seems  to  me,  an 
action  as  instantaneous  as  the  discharge  of  a  Leyden  jar. 

It  cannot  be  said,  in  objection,  that  the  warm  body 
does  not  offer  avenues  enough  for  the  escape  of  the 
caloric,  for  it  is  proved  that  the  pores  of  all  bodies, 
even  of  the  most  solid,  are  so  considerable  in  compari- 
son with  the  space  occupied  by  the  particles  of  those 
bodies,  that  a  fluid  as  rare  as  caloric  is  supposed  to  be 
would  be  able  to  move  about  therein  with  great  free- 


of  Porcelain,  Gilded  and  not  Gilded.          249 

dom.  Besides,  it  often  happens  that  a  very  large  surface 
of  the  warm  body  is  in  contact  with  the  cold  body  ;  but, 
even  in  this  case,  there  is  nothing  in  the  action  taking 
place  in  the  communication  of  the  heat  which  resembles 
in  any  way  the  sudden  explosion  which  takes  place  on 
the  restoration  of  the  equilibrium  among  the  particles 
of  an  elastic  fluid ;  on  the  contrary,  the  slow  and  meas- 
ured progress  of  this  communication,  as  well  as  all  the 
other  phenomena  that  it  presents,  denote  rather  a  grad- 
ual operation,  like  that  which  takes  place  when  the  mo- 
tion of  a  body  is  accelerated  or  retarded. 

The  following  experiment  may  serve  to  explain  and 
confirm  this  important  truth.  If  a  ball  of  iron,  three 
or  four  inches  in  diameter,  fastened  to  a  long  handle  of 
the  same  metal,  be  heated  strongly  in  a  forge  until  it  is 
of  a  whitish-red  heat,  and  then  taken  from  the  fire  and 
plunged  suddenly  into  cold  water,  the  communication 
of  the  heat  to  the  water  will  be  so  far  from  being  instan- 
taneous that  a  considerable  time  will  pass  before  the  ball 
ceases  to  be  red  and  luminous  at  its  surface ;  and  even 
after  the  surface  of  the  ball  has  cooled  so  far  as  no 
longer  to  give  off"  visible  light,  the  interior  will  still  be 
incandescent.  It  is  easy  to  establish  this  last  fact;  for 
if  at  this  point  the  ball  be  taken  from  the  water  and 
held  in  the  air  for  a  few  moments,  the  surface  of  the 
ball  will  again  become  red  and  luminous. 

I  confess  frankly  that  I  have  never  been  able  to  rec- 
oncile these  phenomena  with  that  hypothesis  which  sup- 
poses that  the  increase  of  temperature  of  a  body  is  due 
to  the  accumulation  within  it  of  a  very  rare  and  ex- 
tremely mobile  substance,  especially  when  I  have  con- 
sidered the  great  ease  with  which  such  a  fluid  ought  to 
pass  through  the  pores  of  all  known  bodies. 


250  On  the  Cooling  of  Liquids  in  Vessels  of  Porcelain. 

But  whatever  be  the  explanation  given  to  the  phe- 
nomena which  present  themselves  in  the  heating  and 
cooling  of  bodies,  it  is  certain  that  every  new  fact  relat- 
ing to  these  actions  which  is  discovered  must  tend  to- 
wards perfecting  the  science  of  heat  as  well  as  the  arts 
which  depend  upon  it. 

I  flatter  myself  that  this  Assembly  will  find  the  re- 
sults of  the  experiments  which  I  have  detailed  suffi- 
ciently curious  and  interesting  to  deserve  its  attention. 


AN   ACCOUNT 


CURIOUS    PHENOMENON    OBSERVED    ON    THE 
GLACIERS    OF    CHAMOUNY ; 

TOGETHER    WITH 

SOME  OCCASIONAL  OBSERVATIONS  CONCERNING  THE  PROPA- 
GATION OF  HEAT  IN  FLUIDS. 

IN  an  excursion  which  I  made  the  last  summer,  in  the 
month  of  August,  to  the  glaciers  of  Chamouny,  in 
company  with  Professor  Pictet  of  Geneva,  I  had  an 
opportunity  of  observing,  on  what  is  called  the  Sea  of 
Ice  (Mer  de  Glace),  a  phenomenon  very  common,  as  I 
was  told,  in  those  high  and  cold  regions,  but  which  was 
perfectly  new  to  me,  and  engaged  all  my  attention.  At 
the  surface  of  a  solid  mass  of  ice,  of  vast  thickness  and 
extent,  we  discovered  a  pit  perfectly  cylindrical,  about 
seven  inches  in  diameter  and  more  than  four  feet  deep, 
quite  full  of  water.  On  examining  it  on  the  inside  with 
a  pole,  I  found  that  its  sides  were  polished,  and  that  its 
bottom  was  hemispherical  and  well  defined. 

This  pit  was  not  quite  perpendicular  to  the  plane  of 
the  horizon,  but  inclined  a  little  towards  the  south  as  it 
descended ;  and  in  consequence  of  this  inclination,  its 
mouth,  or  opening  at  the  surface  of  the  ice,  was  not 
circular,  but  elliptical. 

From,  our  guides  I  learned  that  these  cylindrical  holes 
are  frequently  found  on  the  level  parts  of  the  ice  ;  that 
they  are  formed  during  the  summer,  increasing  gradu- 


252  Account  of  a  curious  Phenomenon 

ally  in  depth,  as  long  as  the  hot  weather  continues ;  but 
that  they  are  frozen  up  and  disappear  on  the  return  of 
winter. 

I  would  ask  those  who  maintain  that  water  is  a 
conductor  of  heat,  how  these  pits  are  formed.  On  a 
supposition  that  there  is  no  direct  communication  of 
heat  between  neighbouring  particles  of  that  fluid  which 
happen  to  be  at  different  degrees  of  temperature,  the 
phenomenon  may  easily  be  explained ;  but  it  appears  to 
me  to  be  inexplicable  on  any  other  supposition. 

The  quiescent  mass  of  water  by  which  the  pit  remains 
constantly  filled  must  necessarily  be  at  the  temperature 
of  freezing,  for  it  is  surrounded  on  every  side  by  ice  ; 
but  the  pit  goes  on  to  increase  in  depth  during  the 
whole  summer.  From  whence  comes  the  heat  that 
melts  the  ice  continually  at  the  bottom  of  the  pit  ?  and 
how  does  it  happen  that  this  heat  acts  on  the  bottom  of 
the  pit  only,  and  not  on  its  sides  ? 

These  curious  phenomena  may,  I  think,  be  explained 
in  the  following  manner.  The  warm  winds  which  in 
summer  blow  over  the  surface  of  this  column  of  ice-cold 
water  must  undoubtedly  communicate  some  small  degree 
of  heat  to  those  particles  of  the  fluid  with  which  this 
warm  air  comes  into  immediate  contact;  and  the  par- 
ticles of  the  water  at  the  surface  so  heated,  being  rendered 
specifically  heavier  than  they  were  before  by  this  small 
increase  of  temperature,  sink  slowly  to  the  bottom  of 
the  pit,  where  they  come  into  contact  with  the  ice,  and 
communicate  to  it  the  heat  by  which  the  depth  of  the 
pit  is  continually  increased. 

This  operation  is  exactly  similar  to  that  which  took 
place  in  one  of  my  experiments  (see  my  Essay  on  the 
Propagation  of  Heat  in  Fluids,  Experiment  17),  the 


observed  on  the  Glaciers  of  Chamouny.         253 

results  of  which  no  person  to  my  knowledge  has  yet 
explained. 

There  is  another  very  curious  natural  phenomenon 
which  I  could  wish  to  see  explained  in  a  satisfactory  man- 
ner by  those  who  still  refuse  their  assent  to  the  opinions 
I  have  been  led  to  adopt,  respecting  the  manner  in  which 
heat  is  propagated  in  fluids.  The  water  at  the  bottoms 
of  all  deep  lakes  is  constantly  at  the  same  temperature 
(that  of  41°  Fahrenheit),  summer  and  winter,  with- 
out any  sensible  variation.  This  fact  alone  appears  to 
me  to  be  quite  sufficient  to  prove  that,  if  there  be  any 
immediate  communication  of  heat  between  neighbouring 
particles  or  molecules  of  water,  de  proche  en  proche ^  or 
from  one  of  them  to  the  other,  that  communication  must 
be  so  extremely  slow  that  we  may  with  safety  consider 
it  as  having  no  existence  ;  and  it  is  with  this  limitation 
that  I  beg  to  be  understood  when  I  speak  of  fluids  as 
being  non-conductors  of  heat. 

In  treating  of  the  propagation  of  heat  in  fluids,  I 
have  hitherto  confined  myself  to  the  investigation  of 
the  simple  matter  of  fact,  without  venturing  to  offer 
any  conjectures  relative  to  the  causes  of  the  phenomena 
observed.  But  the  results  of  recent  experiments  on  the 
calorific  and  frigorific  radiations  of  hot  and  of  cold  bodies 
(an  account  of  which  I  shall  have  the  honour  of  laying 
before  the  Royal  Society  in  a  short  time)  have  given 
me  some  new  light  respecting  the  nature  of  heat  and  the 
mode  of  its  communication;  and  I  have  hopes  of  being 
able  to  show  why  all  changes  of  temperature  in  trans- 
parent liquids  must  necessarily  take  place  at  their  sur- 
faces. 

I  have  seen,  with  real  pleasure,  that  several  ingenious 
gentlemen  in  London  and  in  Edinburgh  have  under- 


254  Account  of  a  curious  Phenomenon 

taken  the  investigation  of  the  phenomena  of  the  propa- 
gation of  heat  in  fluids,  and  that  they  have  made  a 
number  of  new  and  ingenious  experiments,  with  a  view 
to  the  further  elucidation  of  that  most  interesting  sub- 
ject. If  I  have  hitherto  abstained  from  taking  public 
notice  of  their  observations  on  the  opinion  I  have 
advanced  on  that  subject  in  my  different  publications, 
it  was  not  from  any  want  of  respect  for  those  gentle- 
men that  I  remained  silent,  but  because  I  still  found  it 
to  be  quite  impossible  to  explain  the  results  of  my  own 
experiments  on  any  other  principles  than  those  which, 
on  the  most  mature  and  dispassionate  deliberation  I  had 
been  induced  to  adopt ;  and  because  my  own  experi- 
ments appeared  to  me  to  be  quite  as  conclusive  (to  say 
no  more  of  them)  as  those  which  were  opposed  to  them  ; 
and,  lastly,  because  I  considered  the  principal  point  in 
dispute,  relative  to  the  passage  of  heat  in  fluids,  as  being 
so  clearly  established  by  the  circumstances  attending  sev- 
eral great  operations  of  nature,  that  this  evidence  did  not 
appear  to  me  to  be  in  danger  of  being  invalidated  by 
conclusions  drawn  from  partial  and  imperfect  experi- 
ments, and  particularly  from  such  as  are  allowed  on  all 
hands  to  be  extremely  delicate. 

In  all  our  attempts  to  cause  heat  to  descend  in  liquids, 
the  heat  unavoidably  communicated  to  the  sides  of  the 
containing  vessel  must  occasion  great  uncertainty  with 
respect  to  the  results  of  the  experiment ;  and  when  that 
vessel  is  constructed  of  ice,  the  flowing  down  of  the 
water  resulting  from  the  thawing  of  that  ice  will  cause 
motions  in  the  liquid,  and  consequently  inaccuracies  of 
still  greater  moment,  as  I  have  found  from  my  own 
experience ;  and  when  thermometers  immersed  in  a 
liquid  at  a  small  distance  below  its  surface  acquire 


observed  on  the  Glaciers  of  Chamouny.         255 

heat  in  consequence  of  a  hot  body  being  applied  to  the 
surface  of  the  liquid,  that  event  is  no  decisive  proof  that 
the  heat  acquired  by  the  thermometer  is  communicated 
by  the  fluid,  from  above,  downwards,  from  molecule  to 
molecule,  de  proche  en  proche ;  so  far  from  being  so,  it  is 
not  even  a  proof  that  it  is  from  the  fluid  that  the  ther- 
mometer receives  the  heat  which  it  acquires ;  for  it  is 
possible,  for  aught  we  know  to  the  contrary,  that  it  may 
be  occasioned  by  the  radiation  of  the  hot  body  placed  at 
the  surface  of  the  fluid. 

In  the  experiments  of  which  I  have  given  an  account 
in  my  Essay  on  the  Propagation  of  Heat  in  Fluids, 
great  masses,  many  pounds  in  weight,  of  boiling-hot 
water,  were  made  to  repose  for  a  long  time  (three  hours) 
on  a  cake  of  ice,  without  melting  but  a  very  small  por- 
tion of  it;  and  on  repeating  the  experiment  with  an 
equal  quantity  of  very  cold  water  (namely,  at  the  tem- 
perature of  41°  Fahrenheit),  nearly  twice  as  much 
ice  was  melted  in  the  same  time.  In  these  experiments 
the  causes  of  uncertainty  above  mentioned  did  not  exist, 
and  the  results  of  them  were  certainly  most  striking. 

The  conclusions  which  naturally  flow  from  those 
results  have  always  appeared  to  me  to  be  so  perfectly 
evident  and  indisputable  as  to  stand  in  no  need  either 
of  elucidation  or  of  further  proof. 

If  water  be  a  conductor  of  heat,  how  did  it  happen 
that  the  heat  in  the  boiling  water  did  not,  in  three  hours, 
find  its  way  downwards  to  the  cake  of  ice  on  which  it 
reposed,  and  from  which  it  was  separated  only  by  a 
stratum  of  cold  water  half  an  inch  in  thickness? 

I  wish  that  gentlemen  who  refuse  their  assent  to  the 
opinions  I  have  advanced  respecting  the  causes  of  this 
curious  phenomenon  would  give  a  better  explanation 


256  Account  of  a  curious  Phenomenon 

of  it  than  that  which  I  have  ventured  to  offer.  I  could 
likewise  wish  that  they  would  inform  us  how  it  happens 
that  the  water  at  the  bottoms  of  all  deep  lakes  remains 
constantly  at  the  same  temperature ;  and  above  all,  how 
the  cylindrical  pits  above  described  are  formed  in  the 
immense  masses  of  solid  and  compact  ice  which  compose 
the  glaciers  of  Chamouny. 

A  remark,  which  surprised  me  not  a  little,  has  been 
made  by  a  gentleman  of  Edinburgh  (Dr.  Thomson), 
on  the  experiments  I  contrived  to  render  visible  the 
currents  into  which  liquids  are  thrown  on  a  sudden 
application  of  heat  or  of  cold.  He  conceives  that  the 
motions  observed  in  my  experiments,  among  the  small 
pieces  of  amber  which  were  suspended  in  a  weak  solution 
of  potash  in  water,  were  no  proof  of  currents  existing  in 
that  liquid ;  as  they  might,  in  his  opinion,  have  been 
occasioned  by  a  change  of  specific  gravity  in  the  amber, 
or  by  air  attached  to  it.  I  am  sorry  that  so  mean  an 
opinion  of  my  accuracy  as  an  observer  should  have  been 
entertained,  as  to  imagine  that  I  could  have  been  so 
easily  deceived.  For  nothing,  surely,  is  easier  than  to 
distinguish  the  motion  of  a  solid  suspended  in  a  liquid 
of  the  same  specific  gravity,  which  is  carried  along  by  a 
current  in  the  liquid,  from  that  of  a  body  which  descends, 
or  ascends,  in  the  liquid  in  consequence  of  its  relative 
weight  or  levity.  In  the  one  case  the  motion  is  uni- 
form ;  in  the  other,  it  is  accelerated.  In  a  current  the 
body  may  be  carried  forward  in  all  directions,  and 
even  in  curved  lines  ;  but  when  it  falls  in  a  quiescent 
fluid  by  the  action  of  gravity,  or  rises  in  consequence  of 
its  being  specifically  lighter  than  the  fluid,  it  must  neces- 
sarily move  in  a  vertical  direction. 

The  fact  is,  that  I  very  often  observed,  in  the  course 


observed  on  the  Glaciers  of  Chamouny.         257 

of  my  numerous  experiments,  the  motions  of  small  par- 
ticles of  matter  of  different  kinds  in  water,  which  Dr. 
Thomson  describes  ;  but  so  far  from  inferring /row  them 
the  existence  of  currents  in  that  fluid,  their  cause  was  so 
perfectly  evident  that  I  did  not  even  think  it  necessary 
to  make  any  mention  of  them. 

I  cannot  conclude  this  paper  without  requesting  that 
the  Royal  Society  would  excuse  the  liberty  I  have  taken 
in  troubling  them  with  these  remarks.  Very  desirous 
of  avoiding  every  species  of  altercation,  I  have  hitherto 
cautiously  abstained  from  engaging  in  literary  disputes  ; 
and  I  shall  most  certainly  endeavour  to  avoid  them  in 
future. 

I  am  responsible  to  the  public  for  the  accuracy  of 
the  accounts  which  I  have  published  of  my  experiments; 
but  it  cannot  reasonably  be  expected  that  I  should 
answer  all  the  objections  that  may  be  made  to  the  con- 
clusions which  I  have  drawn  from  them.  It  will,  how- 
ever, at  all  times,  afford  me  real  satisfaction  to  see  my 
opinions  examined  and  my  mistakes  corrected  ;  for  my 
first  and  most  earnest  wish  is,  to  contribute  to  the 
advancement  of  useful  knowledge. 

[This  paper  is  printed  from  the  Philosophical  Transactions  of  the 
Royal  Society,  XCIV.  (1804),  pp.  23  -  29.] 


VOL.    II. 


AN   ACCOUNT 


SOME    NEW   EXPERIMENTS    ON    THE   TEMPERATURE 
OF   WATER   AT   ITS   MAXIMUM   DENSITY. 

IN  my  seventh  Essay  on  the  Propagation  of  Heat 
in  Fluids,  and  in  a  paper  published  in  the  Philo- 
sophical Transactions  for  the  year  1804,  in  which  I  have 
given  an  account  of  a  curious  phenomenon  frequently  ob- 
served on  the  glaciers  of  Chamouny,  I  have  ascribed  the 
melting  of  the  ice  below  the  surface  of  the  ice-cold  water 
to  currents  of  water  slightly  warmer,  and  consequently 
slightly  heavier,  which  descend  from  the  surface  to  the 
bottom  of  the  ice-cold  water;  but  the  principal  fact  on 
which  this  supposition  is  founded  having  been  called 
in  question  by  various  persons,  I  have  endeavoured  to 
establish  it  by  new  and  decisive  experiments. 

If  it  is  true  that  the  temperature  of  water  at  its  maxi- 
mum density  is  considerably  higher  than  the  freezing- 
point  of  that  liquid  (as  was  announced  many  years  ago 
by  M.  de  Luc),  and  that  the  communication  of  heat  in 
liquids  is  brought  about  by  a  movement  of  circulation 
caused  by  a  change  of  density  in  the  particles  of  the 
fluid  resulting  from  a  change  of  temperature,  the  ex- 
planation that  I  have  given  of  the  phenomenon  of  the 
melting  of  ice  covered  with  a  layer  of  ice-cold  water  by 
heat  applied  to  the  surface  of  the  water,  would  seem 


The  Temperature  of  Water,  etc.  259 

natural  and  admissible  ;  but  if  the  density  of  water  is 
greater  at  the  temperature  of  melting  ice  than  at  any 
other  more  elevated  temperature,  as  some  philosophers 
assert,  it  is  evident  that  the  vertical  descending  currents 
of  warm  water  which  I  have  described  cannot  exist,  and 
my  explanation  must  be  rejected. 

This  inquiry  interested  me  all  the  more,  because  the 
fact  in  question  had  served  as  the  foundation  of  the 
theory  which  I  gave  in  my  seventh  Essay  on  the  pe- 
riodical winds  of  the  polar  regions,  and  as  the  basis  of 
my  conjectures  on  the  existence  of  currents  of  cold  water 
in  the  depths  of  the  sea  coming  from  the  polar  regions 
to  the  equator,  and  on  the  cause  of  the  great  difference 
which  is  found  in  the  temperature  of  different  countries 
situated  in  the  same  latitude  and  at  the  same  height 
above  the  level  of  the  sea. 

After  meditating  on  the  means  which  I  should  employ 
to  establish  this  important  fact  beyond  doubt,  I  thought 
of  the  experiment  which  I  am  about  to  describe,  and 
which  is  all  the  more  interesting,  since  it  not  only 
demonstrates  the  existence  in  a  mass  of  water  which  is 
warmed  or  cooled,  of  the  currents  assumed  by  my 
theory,  but  proves  at  the  same  time  that  the  temper- 
ature at  which  the  density  of  water  is  at  a  maximum  is 
actually  some  degrees  above  that  of  melting  ice. 

Having  provided  a  cylindrical  vessel  (A,  Plate  VI.), 
open  above,  made  of  thin  sheet  brass,  5^  inches  in 
diameter  and  4  inches  deep,  supported  on  three  strong 
legs  \\  inches  high,  I  placed  in  it  a  thin  brass  cup 
(B)  2  inches  in  diameter  at  its  bottom  (which  is  a 
little  convex  downwards),  2^  inches  wide  at  its  brim, 
and  IT\  inches  deep;  this  cup  stands  on  three  spread- 
ing legs  made  of  strong  brass  wire,  and  of  such  form 


260  The  Temperature  of  Water 

and  length  that  when  the  cup  is  introduced  into  the 
cylindrical  vessel,  it  remains  firmly  fixed  in  the  axis  of 
it,  and  in  such  a  situation  that  the  bottom  of  the  cup 
is  elevated  just  i^  inches  above  the  bottom  of  the 
cylindrical  vessel. 

In  the  middle  of  this  cup  there  stands  a  vertical  tube 
of  thin  sheet  brass  J  of  an  inch  in  diameter  and  T67  of  an 
inch  in  length,  open  above,  which  serves  as  a  support 
for  another  smaller  cup  (C),  which  is  made  of  cork,  the 
brim  of  which  is  on  the  same  horizontal  level  with  the 
brim  of  the  larger  brass  cup  in  which  it  is  placed. 

This  cork  cup,  which  is  spherical,  being  something 
less  than  half  of  an  hollow  sphere,  is  I  inch  in  diameter 
at  its  brim,  measured  within,  T%  of  an  inch  deep,  and  \ 
of  an  inch  in  thickness.  It  is  firmly  attached  to  the  ver- 
tical tube  on  which  it  stands,  by  means  of  a  cylindrical 
foot  J  of  an  inch  in  diameter  and  \  of  an  inch  high, 
which  enters  with  friction  into  the  opening  of  the  vertical 
tube. 

On  one  side  of  this  cork  cup  there  is  a  small  opening, 
which  receives  and  in  which  is  confined  the  lower  ex- 
tremity of  the  tube  of  a  small  mercurial  thermometer 
(D).  The  bulb  of  this  thermometer,  which  is  spheri- 
cal, is  T3¥  of  an  inch  in  diameter,  and  it  is  so  fixed  in 
the  middle  of  the  cup,  that  its  centre  is  \  of  an  inch 
above  the  bottom  of  the  cup ;  consequently  it  does 
not  touch  the  cup  anywhere,  nor  does  any  part  of  it 
project  above  the  level  of  its  brim. 

The  tube  of  this  thermometer,  which  is  6  inches  in 
length,  has  an  elbow  near  its  lower  end  at  the  distance 
of  i  inch  from  its  bulb,  which  elbow  forms  an  angle 
of  about  no  degrees,  and  the  thermometer  is  so  fixed 
in  the  cork  cup,  that  the  short  branch  of  its  tube,  namely, 


at  its  Maximum  Density.  261 

that  to  the  end  of  which  the  bulb  is  attached,  lies  in  an 
horizontal  position,  while  the  longer  branch  (to  which  a 
scale  made  of  ivory  and  graduated  according  to  Fahren- 
heit is  affixed)  projects  obliquely  upwards  and  outwards 
in  such  a  manner  that  the  freezing-point  of  the  scale  lies 
just  above  the  level  of  the  top  of  the  cylindrical  vessel 
in  which  the  cups  are  placed. 

The  cork  cup,  which  was  turned  in  the  lathe,  is  neatly 
formed,  and  in  order  to  close  the  pores  of  the  cork,  it 
was  covered  within  and  without  with  a  thin  coating  of 
melted  wax,  which  was  polished  after  the  wax  was  cold. 

The  thermometer  was  fixed  to  the  cork  cup  by  means 
of  wax,  and  in  doing  this  care  was  taken  to  preserve  the 
regular  form  of  the  cup,  both  within  and  without. 

The  vertical  brass  tube  which  supports  this  cup  in 
the  axis  of  the  brass  cup  is  pierced  with  several  small 
holes,  in  order  to  allow  the  water  employed  in  the  ex- 
periments to  pass  freely  into  and  through  it. 

Having  attached  about  6  ounces  of  lead  to  each  of 
the  legs  of  the  brass  cup,  in  order  to  render  it  the  more 
steady  in  its  place,  it  was  now  introduced  with  its  con- 
tents into  the  cylindrical  vessel,  and  the  vessel  was  placed 
in  an  earthen  basin  (E),  and  surrounded  on  all  sides  with 
pounded  ice.  This  basin  was  1 1  inches  in  diameter  at 
its  brim,  7  inches  in  diameter  at  the  bottom,  and  5  inches 
deep,  and  was  placed  on  a  firm  table  in  a  quiet  room. 

Several  cakes  of  ice  were  then  placed  under  the  bottom 
of  the  brass  cup,  and  the  cup  was  surrounded  on  all 
sides  by  a  circular  row  of  other  long  pieces  of  ice  fixed 
in  a  vertical  position  between  the  outer  walls  of  the  cup 
and  the  walls  of  the  cylindrical  vessel.  These  pieces 
were  about  4  inches  long,  and  extended  from  the  bottom 
of  the  vessel  to  within  a  very  short  distance  of  the  top. 


262  The  Temperature  of  Water 

All  these  pieces  of  ice  having  been  fixed  firmly  in  their 
places  by  means  of  some  little  wooden  wedges,  ice-cold 
water  was  poured  into  the  cylindrical  vessel  until  the 
surface  of  this  liquid  was  an  inch  above  the  upper  edge 
of  the  cork  cup. 

In  this  state  of  things  it  is  evident  that  the  two  cups 
were  filled  with  and  surrounded  on  all  sides  by  water  at 
the  temperature  of  melting  ice,  and  that  this  temperature 
was  maintained  constant  by  the  pieces  of  ice  with  which 
the  water  was  in  contact. 

After  having  left  the  apparatus  in  this  situation  for 
about  an  hour,  in  order  to  satisfy  myself  that  the  tem- 
perature of  the  cold  water  was  constant  and  uniform 
throughout  its  entire  mass,  I  made  the  following  experi- 
ment. 

Experiment  No.  i.  —  A  solid  ball  of  tin  (F)  having 
been  provided,  2  inches  in  diameter,  with  a  cylindrical 
projection  on  the  lower  side  of  it,  i  inch  in  diameter 
and  J  of  an  inch  long  ending  in  a  conical  point  which 
projected  (downwards)  |-  of  an  inch  farther,  and  having 
on  the  other  side  a  strong  iron  wire  6  inches  long,  which 
served  as  a  handle,  —  this  ball,  after  having  been  im- 
mersed for  half  an  hour  in  a  considerable  quantity  of 
water  at  the  temperature  of  42°  F.,  was  withdrawn  from 
the  water,  wiped  dry  with  a  handkerchief  of  the  same 
temperature,  placed  without  loss  of  time  above  the 
cylindrical  vessel,  and  fixed  in  such  a  position  that  the 
entire  conical  point  of  the  tin  ball  (|  of  an  inch  in  length) 
was  submerged  in  the  cold  water  contained  in  the  vessel. 

To  fix  and  keep  the  metallic  ball  in  its  place,  I  used  a 
strong  slip  of  tin  (GH),  6  inches  long  and  2j-  inches 
wide,  with  a  circular  hole  in  the  middle  of  it  i  inch 
in  diameter.  This  slip  of  tin  being  laid  horizontally  on 


at  its  Maximum  Density.  263 

the  top  or  brim  of  the  cylindrical  vessel  in  such  a  manner 
that  the  centre  of  the  circular  hole  coincided  with  the 
axis  of  the  cylindrical  vessel,  when  the  short  cylindrical 
projection  belonging  to  the  ball  was  introduced  into  that 
hole,  the  ball  was  firmly  supported  in  its  proper  place. 

The  ball  was  placed  in  such  a  position  that  the  end  of 
the  conical  projection  was  immediately  over  the  cork  cup, 
at  the  distance  of  \\  inches  above  the  level  of  its  brim 
and  consequently  J  of  an  inch  above  the  upper  part  of 
the  bulb  of  the  small  thermometer  which  lay  in  this  cup. 

The  quantity  of  cold  water  in  the  cylindrical  vessel 
had  been  so  regulated  beforehand  that  when  the  conical 
point  was  entirely  submerged,  the  surface  of  the  water 
was  on  a  level  with  the  base  of  this  inverted  cone,  so 
that  the  whole  of  the  cylindrical  part  of  the  projection 
was  out  of  the  water. 

I  knew  that  the  particles  of  ice-cold  water  which  were 
tjius  brought  into  contact  with  the  conical  point  could 
not  fail  to  acquire  some  small  degree  of  heat  from  that 
relatively  warm  metal,  and  I  concluded  that  if  the  par- 
ticles of  water  so  warmed  should  in  fact  become  heavier 
than  they  were  before,  in  consequence  of  this  small 
increase  of  temperature,  they  must  necessarily  descend  in 
the  surrounding  lighter  ice-cold  liquid,  and  as  the  heated 
metallic  point  was  placed  directly  over  the  cork  cup, 
and  fixed  immovably  in  that  situation,  I  foresaw  that 
the  descending  current  of  warm  water  must  necessarily 
fall  into  that  cup  and  at  length  fill  it,  and  that  the  pres- 
ence of  this  warm  water  in  the  cup  would  be  announced 
by  the  rising  of  the  thermometer. 

The  result  of  this  very  interesting  experiment  was 
just  what  I  expected:  the  conical  metallic  point  had  not 
been  in  contact  with  the  ice-cold  water  more  than  20 


264  The  Temperature  of  Water 

seconds  when  the  mercury  in  the  thermometer  began  to 
rise,  and  in  3  minutes  it  had  risen  three  degrees  and 
a  half,  namely,  from  32°  to  35^°;  when  5  minutes  had 
elapsed  it  had  risen  to  36°. 

Another  small  thermometer  placed  just  below  the 
surface  of  the  ice-cold  water,  and  only  T2Q-  of  an  inch  from 
the  upper  part  of  the  conical  point  and  on  one  side  of 
it,  did  not  appear  to  be  sensibly  affected  by  the  vicinity 
of  that  warm  body. 

A  third  thermometer,  the  bulb  of  which  was  placed 
in  the  brass  cup  just  on  the  outside  of  the  cork  cup  and 
on  a  level  with  its  brim,  showed  that  the  water  which 
immediately  surrounded  the  cork  cup  remained  con- 
stantly at  the  temperature  of  freezing  during  the  whole 
time  that  the  experiment  lasted. 

As  I  well  knew  from  the  results  of  the  experiments 
on  the  propagation  of  heat  in  a  solid  bar  of  metal,*  that 
no  one  of  the  particles  of  cold  water  in  contact  with  the 
surface  of  the  conical  projection,  in  the  experiment  which 
I  have  just  described,  could  acquire  by  this  momentary 
contact  a  temperature  as  high  as  that  of  the  warm  metal, 
I  was  by  no  means  surprised  to  find  that  the  thermom- 
eter belonging  to  the  cork  cup  rose  no  higher  than  36°. 

In  order  to  see  if  it  could  not  be  made  to  rise  not 
only  higher,  but  also  more  rapidly,  by  employing  the 
metallic  ball  heated  to  such  a  temperature  as  it  might  be 
supposed  would  be  sufficient  to  heat  those  particles  of 
ice-cold  water  which  should  come  into  contact  with  its 
conical  point,  to  the  temperature  at  which  the  density 
of  water  is  supposed  to  be  a  maximum,  I  made  the 
following  experiment. 

*  An  account  of  these  experiments  has  been  given  in  a  memoir  presented  to  the 
Mathematical  and  Physical  Class  of  the  National  Institute  of  France,  on  the  yth  of 
May,  1804.  See  also  p.  144. 


at  its  Maximum  Density.  265 

Experiment  No.  2.  —  Having  removed  the  ball,  I  gently 
brushed  away  the  warm  water  which  in  the  last  experi- 
ment had  been  lodged  in  the  cavity  of  the  cork  cup,  and 
which  still  remained  there,  as  was  evident  from  the  indi- 
cation of  the  thermometer  belonging  to  the  cup  ;  I  then 
placed  several  small  cakes  of  ice  in  the  cylindrical  vessel, 
which  ice,  floating  on  the  surface  of  the  water  in  the  ves- 
sel, prevented  the  water  from  receiving  heat  from  the 
surrounding  air,  which  at  that  time  was  at  the  temper- 
ature of  70°  F.  As  the  cork  cup  had  been  a  little  heated 
by  the  warm  water  in  the  foregoing  experiment,  time 
was  now  given  it  to  cool. 

As  soon  as  the  cup  and  the  whole  mass  of  the  water 
in  the  cylindrical  vessel  appeared  to  have  acquired  the 
temperature  of  freezing,  I  carefully  removed  the  cakes 
of  ice  which  floated  on  the  surface  of  the  water,  and  in- 
troduced once  more  the  projecting  conical  point  belong- 
ing to  the  metallic  ball  into  the  ice-cold  water  in  the 
vessel,  placing  it  exactly  in  the  same  place  which  it  had 
occupied  in  the  foregoing  experiment ;  but  this  ball, 
instead  of  being  at  the  temperature  of  42°  F.,  as  before, 
was  now  at  the  temperature  of  60°  F. 

The  results  of  this  experiment  were  very  striking, 
and,  if  I  am  not  much  mistaken,  afford  a  direct,  unex- 
ceptionable, and  demonstrative  proof,  not  only  that  the 
maximum  of  the  density  of  water  is  in  fact  at  a  temper- 
ature which  is  several  degrees  above  the  point  of  freezing, 
but  also  that  warm  currents  do  actually  set  downwards 
in  ice-cold  water,  whenever  a  certain  small  degree  of 
heat  is  applied  to  the  particles  of  that  fluid  which  are  at 
its  surface,  as  I  have  already  announced  in  my  Essay  on 
the  Propagation  of  Heat  in  Fluids. 

The  conical  metallic  point  had  been  in  its  place  no 


266  The  Temperature  of  Water 

more  than  10  seconds  when  I  distinctly  saw  that  the 
mercury  in  the  thermometer  belonging  to  the  cork  cup 
was  in  motion,  and,  when  50  seconds  had  elapsed,  it  had 
risen  four  degrees,  viz.  from  32°  to  36°. 

When  2  minutes  and  30  seconds  had  elapsed,  reckon- 
ing from  the  moment  when  the  metallic  point  was  intro- 
duced into  the  cold  water,  the  thermometer  had  risen 
to  39°,  and  at  the  end  of  6  minutes  to  39^-°,  when  it  began 
to  fall ;  but  very  slowly,  however,  for  at  the  end  of  8 
minutes  and  30  seconds  it  was  at  39!°. 

A  small  mercurial  thermometer,  the  bulb  of  which 
was  placed  on  one  side  of  the  cork  cup  at  the  distance 
of  about  y2Q-  of  an  inch  from  it,  showed  no  signs  of  being 
in  the  least  affected  by  the  vertical  current  of  warm  water 
which  descended  from  the  conical  point  into  the  cup  in 
this  experiment. 

This  experiment  was  repeated  four  times  the  same 
day  (the  I3th  of  June,  1805),  and  always  with  nearly 
the  same  results.  The  mean  results  of  these  four  ex- 
periments were  as  follows  :  — 


Time  elapsed,  reckoned 
from  the  beginning  of 
the  experiment. 

m.           s. 
O            O 

Temperature  < 
water   in   the 
cup,   as   show 
the  thermom 
Degrees. 

At 

o 

10 

began  to  rise     32+ 

At 

0 

23 

had  risen  to          .          .         .         .         -33 

0 

28  ' 

"      "     "       34 

0 

35 

"      "     "          35 

0 

48 

"      "     "      36 

I 

3 

"      "     "           37 

I 

35 

«      «     «      38 

2 

32 

"      "     "          39 

3 

41 

•«««««      391 

4 

48 

"      "     "          392 

6 

5 

"      "     "     391 

at  its  Maximum  Density.  267 

As  I  had  found  by  some  of  my  experiments  made  in 
the  year  1797  (of  which  an  account  is  given  in  my 
seventh  Essay,  Part  I.)  that  water  at  the  temperature  of 
about  42°  F.,  and  .consequently  what  we  should  call  very 
cold,  melted  considerably  more  ice,  when  standing  on  it, 
than  an  equal  quantity  of  boiling-hot  water  in  the  same 
situation,  I  was  very  curious  to  see  whether  the  ther- 
mometer, the  bulb  of  which  lay  in  the  cork  cup,  would 
not  also  be  less  heated  by  the  ball  when  it  should  be 
applied  very  hot  to  the  surface  of  the  water,  than  when 
its  temperature  was  much  lower. 

Seeing  that  this  research  ought  to  throw  great  light  on 
the  mysterious  operations  of  the  distribution  of  heat 
in  liquids,  I  hastened  to  make  the  following  experiment. 

Experiment  No.  3. —  The  cylindrical  vessel  with  its 
contents  having  been  once  more  reduced  to  the  uniform 
temperature  of  freezing  water,  the  metallic  ball  was  heated 
in  boiling  water,  and  being  as  expeditiously  as  possible 
taken  out  of  that  hot  liquid,  its  projecting  conical  point 
was  suddenly  submerged  in  the  ice-cold  water,  as  in  the 
former  experiments. 

The  result  of  this  experiment  was  very  interesting. 
It  was  not  till  50  seconds  had  elapsed  that  the  ther- 
mometer began  to  show  any  signs  of  rising,  and  at  the 
end  of  i  minute  and  7  seconds  it  had  risen  only  2 
degrees. 

In  the  foregoing  experiment,  when  the  metallic  ball 
was  so  much  colder,  the  thermometer  began  to  rise  in 
10  seconds,  and  at  the  end  of  I  minute  and  3  seconds  it 
had  risen  5  degrees. 

This  difference  is  very  remarkable,  and  if  it  does  not 
prove  the  existence  and  great  efficacy  of  currents  in  con- 
veying heat  in  fluids,  I  must  confess  that  I  do  not  see 


268  The  Temperature  of  Water 

how  the  existence  of  any  invisible  mechanical  operation, 
the  progress  of  which  does  not  immediately  fall  under 
the  cognizance  of  our  senses,  can  ever  be  demonstrated. 
As  the  experiment  made  with  the  ball  heated  in  boil- 
ing water  appeared  to  me  to  be  very  interesting,  I 
repeated  it  twice,  and  its  results  were  always  nearly  the 
same.  The  mean  results  of  these  three  experiments 
were  as  follows  :  — 


Time  elapsed,  reckoned                                                                                              Temperature  of  the 
from   the   beginning  of                                                                                                   water    in   the   cork 
the  experiment.                                                                                                     cup,   as  shown   by 
the  thermometer. 

m. 

s. 

Degrees. 

O 

O 

At 

O 

5° 

the  thermometer  began  to  rise          .         .         32+ 

At 

I 

2 

had  risen  to      33 

I 

7 

"       "      "          34 

I 

18 

2 

2 

"       "      "           36 

3 

2 

"      "      36i 

4 

17 

"      "      "          37 

6 

12 

"      "      "      38 

7 

'7 

"      "      "           38^ 

0 

0 

"       «      "                                                            784- 

14       o       ****•*.        .       .        .        .       .    38^ 

By  comparing  the  mean  results  of  these  experiments 
with  the  mean  results  of  those  in  which  the  ball  was  at 
the  temperature  of  60°  or  less,  we.  may  see  how  much 
more  rapid  the  communication  of  heat  in  the  cold  water 
from  above  downwards  was  when  the  metallic  ball  was 
relatively  cold  than  when  it  was  much  warmer  ;  but  we 
must  not  consider  of  too  much  importance  the  deter- 
mination of  the  relative  rapidity  thus  made,  because  it 
is  more  than  probable  that  it  was  not  till  after  the 
conical  metallic  point  had  been  considerably  cooled  by 


at  its  Maximum  Density.  269 

contact  with  the  cold  water  that  the  vertical  descending 
currents  could  exist  by  which  the  thermometer  was  at 
length  heated.  At  the  beginning  of  the  experiment 
made  with  the  tin  ball  warmed  in  boiling  water,  the 
particles  of  water  which  were  in  immediate  contact  with 
the  conical  point  while  it  was  still  very  warm,  were 
heated  to  a  temperature  higher  than  that  at  which  the 
density  of  water  is  at  a  maximum,  and  the  density  of 
these  particles  being  diminished  by  this  high  degree  of 
heat,  the  vertical  currents  in  the  cold  water  were  at  the 
beginning  ascending  currents,  as  I  satisfied  myself  by 
means  of  a  small  thermometer  placed  by  the  side  of  the 
conical  point  at  a  distance  of  T2¥  of  an  inch  from  its  base, 
and  immediately  below  the  surface  of  the  cold  water : 
this  thermometer  began  to  rise  very  rapidly  as  soon  as 
the  warm  metallic  point  was  plunged  into  the  cold 
water. 

Another  small  thermometer,  the  bulb  of  which  was 
situated  at  about  the  same  distance  from  the  axis  of  the 
conical  projection,  but  -J-  of  an  inch  below  the  surface  of 
the  cold  water,  preserved  throughout  the  entire  experi- 
ment the  appearance  of  perfect  rest. 

The  results  of  this  last  experiment  are  all  the  more 
interesting  because  they  afford  a  demonstrative  proof  that 
it  was  neither  by  a  direct  communication  of  heat  in  the 
water,  which  was  at  rest,  from  molecule  to  molecule,  de 
proche  enproche,  nor  by  calorific  radiations  passing  through 
the  water,  that  heat  was  communicated  from  the  metallic 
point  to  the  bulb  of  the  thermometer,  but  actually  by  a 
descending  current  of  warm  water  ;  for  it  is  perfectly 
evident  that  if  this  heat  had  been  communicated  either 
by  a  direct  transfer  in  the  water  from  molecule  to  mole- 
cule or  by  calorific  radiations  passing  from  the  surface 


2  70  The  Temperature  of  Water 

of  the  metal  through  the  water,  which  remained  at  rest, 
this  communication  would  naturally  have  been  the  most 
rapid  when  the  metallic  point  was  the  warmest.  What 
did  take  place  was  exactly  contrary  to  this,  as  we  have 
just  seen.  Moreover,  the  small  thermometer,  which 
was  placed  close  to  the  metallic  body  on  one  side,  and 
which  in  this  experiment  was  in  no  degree  affected  by 
the  heat  of  this  body,  would  not  have  failed  to  acquire 
as  much  heat  at  least  as  that  placed  in  the  cork  cup,  which 
was  situated  below  the  metallic  body  and  at  a  greater 
distance  from  it. 

The  considerable  amount  of  time  which  elapsed  in  the 
experiments  performed  with  the  tin  ball  heated  in  boil- 
ing water  before  the  thermometer  in  the  cork  cup  began 
to  be  so  sensibly  affected,  and  the  rapidity  with  which  it 
was  then  warmed  through  several  degrees  as  soon  as  it 
began  to  rise,  indicate  a  fact  which  it  is  important  to 
notice.  In  order  to  throw  light  upon  this  fact,  we 
must  consider  carefully  the  operation  of  the  heating  of 
cold  water  by  the  warm  metallic  surface  with  which  it 
was  in  contact,  and  examine  it  in  its  progress  and  in 
all  its  details. 

Let  us  begin  by  supposing  that  the  conical  point  of 
the  ball,  at  the  temperature  of  boiling  water,  has  just 
been  submerged  vertically  up  to  the  level  of  its  base  in 
a  mass  of  undisturbed  water  at  the  temperature  of  melt- 
ing ice.  As  the  particles  of  water,  which  in  this  case 
are  in  contact  with  the  warm  metallic  surface,  cannot 
pass,  all  of  a  sudden,  from  the  temperature  of  melting 
ice  to  that  of  boiling  water  without  passing  through  all 
the  intermediate  degrees,  and  since  these  particles  at  the 
temperature  of  melting  ice  cannot  become  warmer  with- 
out becoming  more  dense,  it  is  evident  that  they  must 


at  its  Maximum  Density.  271 

have  a  tendency  to  descend,  and  consequently  to  leave 
the  surface  of  the  metal,  as  soon  as  they  begin  to  acquire 
heat ;  but  experiment  showed  that,  instead  of  descend- 
ing, they  were  actually  pushed  upwards :  this  proves 
that  they  were  heated  so  rapidly  that,  before  they  had 
time  to  leave  the  surface  of  the  metal  and  to  escape 
from  its  calorific  influence,  they  had  acquired  a  temper- 
ature so  elevated  that  their  density,  after  having  passed 
rapidly  the  point  of  its  maximum,  became  even  less  than 
it  was  at  the  temperature  of  melting  ice.  But  after 
some  moments,  the  metallic  body  having  cooled  some- 
what, and  the  communication  of  heat  to  the  particles  of 
water  taking  place  more  slowly,  these  particles,  having 
become  more  dense  on  account  of  a  slight  increase 
of  temperature,  had  time  to  escape  before  becoming 
warmer,  and  at  that  time  the  descending  current  sud- 
denly began. 

This  fact  interests  me  the  more,  as  it  may  serve  in 
some  sort  to  explain  a  phenomenon  which  I  observed  in 
an  experiment  made  eight  years  ago,  an  account  of 
which  I  gave  in  my  Essay  on  the  Propagation  of  Heat 
in  Fluids.* 

The  phenomenon  to  which  I  have  alluded  was  this : 
Having  poured  some  mercury  into  a  small  cylindrical 
glass  vessel  2  inches  in  diameter  and  3-|-  inches  deep, 
until  this  fluid  filled  the  vessel  to  the  height  of  an  inch, 

1  poured  on  to  the  mercury  twice  as  much  water  (that  is, 

2  inches),  and,  plunging  the  vessel  up  to  the  level  of  the 
upper  surface  of  the  mercury  into  a  freezing  mixture  of 
pounded   ice  and  sea-salt,   the  temperature  of  the  air 
being  60°  F.,   I   allowed  the  whole  to  cool  quietly,  in 
order  to  see  in  what  part  of  the  water  the  ice  would  first 

*  See  Vol.  I.  p.  357. 


272  The  Temperature  of  Water 

appear.  It  was  at  the  bottom  of  the  water,  where  this 
liquid  was  in  contact  with  the  mercury,  that  the  ice 
formed. 

The  layer  of  water  which  rested  immediately  on  the 
surface  of  the  mercury  having  been  cooled  to  about  the 
temperature  of  41°  F.,  where  the  density  of  water  is  at 
its  maximum,  the  particles  of  this  water,  which  were 
then  in  immediate  contact  with  the  mercury,  losing  still 
more  of  their  heat,  became  of  necessity  less  dense,  and 
had  consequently  a  tendency  to  leave  the  bottom  of  the 
water  and  to  ascend  upwards ;  but  the  rapidity  with 
which  they  were  cooled  by  the  mercury  was  so  great 
that  they  were  frozen  before  they  could  escape  from  the 
cooling  influence  of  this  cold  body. 

After  all  that  I  have  said  about  the  warm  and  cold 
currents  which  take  place  in  a  liquid  which  is  warmed 
or  cooled,  it  might  perhaps  be  thought  that  I  regard 
these  currents  as  composed  of  single  particles  of  the 
liquid,  which,  having  been  in  immediate  contact  with 
the  body  which  gives  or  which  receives  the  heat,  are 
all  of  the  same  temperature.  I  am  all  the  farther  from 
holding  this  opinion,  since  I  know  from  the  results 
of  several  experiments  made  expressly  for  elucidating 
this  point,  (and  which  I  shall  have  the  honor  of  present- 
ing to  the  Class  on  another  occasion,)  that  a  liquid 
current  cannot  pass  through  another  liquid  mass  which 
is  at  rest,  and  which  is  of  the  same  kind  and  of  about 
the  same  specific  gravity,  without  producing  a  per- 
ceptible mixture  of  the  two  liquids  ;  much  less,  therefore, 
can  a  small  current  of  warm  water  pass  without  mixing 
through  a  mass  of  cold  water  ;  and  the  farther  it  advances 
the  more  it  will  be  mixed,  and  the  more,  in  consequence, 
will  its  temperature  be  found  to  be  lowered. 


at  its  Maximum  Density.  273 

For  example,  in  the  experiments  of  which  I  have  just 
given  an  account,  the  cork  cup,  which  received  the 
current  of  warm  water  descending  from  the  metallic 
point  of  the  tin  ball,  was  only  \  of  an  inch  below  the 
extremity  of  this  point ;  if  this  distance  had  been  greater, 
the  thermometer  in  the  cup  would  certainly  have  risen 
to  a  less  height :  for  this  reason  these  experiments  ought 
not  to  be  regarded  as  suitable  for  determining  with  great 
exactness  the  temperature  at  which  the  density  of  water 
is  at  a  maximum,  but  rather  as  proving  that  this  tem- 
perature is  really  several  degrees  of  the  thermometric 
scale  above  that  of  melting  ice;  and  this  is  all  that  I  am 
particularly  interested  in  showing  at  the  present  time. 

Judging  from  the  constant  temperature  which  is  found 
at  all  seasons  at  the  bottom  of  deep  lakes  and  from  the 
results  of  several  direct  experiments,  we  may  conclude 
that  water  is  at  its  maximum  density  when  it  is  at  the 
temperature  of  about  41°  of  Fahrenheit's  scale,  which 
corresponds  to  4°  on  that  of  Reaumur,  and  to  5°  of  the 
Centigrade  scale. 

[This  paper  is  translated  from  the  Memoires  de  1'Institut,  etc.,  VII. 
(1806),  pp.  78-97.  The  greater  part  of  the  translation  is  taken  from 
Nicholson's  Journal,  XI.  (1805),  pp.  225-235.] 


18 


INQUIRIES 

CONCERNING 

THE   MODE  OF   THE   PROPAGATION   OF  HEAT   IN 
LIQUIDS. 

THE  motions  in  fluids  which  result  from  a  change 
in  their  temperature  give  rise  to  so  great  a  number 
of  phenomena,  that  philosophers  cannot  bestow  too 
much  pains  in  investigating  that  interesting  branch  of 
knowledge. 

When  heat  is  propagated  in  solid  bodies,  it  passes 
from  particle  to  particle,  de  proche  en  proche ,  and  appar- 
ently with  the  same  celerity  in  every  direction  ;  but  it 
is  certain  that  heat  is  not  transmitted  in  the  same  manner 
in  fluids. 

When  a  solid  body  is  heated  and  plunged  in  a  cold 
liquid,  the  particles  of  the  liquid  in  contact  with  the 
body,  being  rarefied  by  the  heat  that  they  receive  from 
it,  and  being  rendered  specifically  lighter  than  the  sur- 
rounding particles,  are  forced  to  give  place  to  these  last 
and  to  rise  to  the  surface  of  the  liquid  ;  and  the  cold  par- 
ticles that  replace  them  at  the  surface  of  the  hot  body, 
being  in  their  turn  heated,  rarefied,  and  forced  up,  — all 
the  particles  thus  heated  by  a  successive  contact  with 
the  hot  body  form  a  continued  ascending  current, 
which  carries  the  whole  of  the  heat  immediately  towards 
the  surface  of  the  liquid,  so  that  the  strata  of  the  liquid 
situated  at  a  small  distance  under  the  hot  body  are  not 
sensibly  heated  by  it. 


Inquiries  concerning  the  Mode,  etc.  275 

When  a  solid  body  is  plunged  in  a  liquid  which  is 
hotter  than  the  body,  the  particles  of  the  liquid  in  con- 
tact with  the  body,  being  condensed  by  the  cooling  they 
undergo,  descend,  in  consequence  of  the  increase  of 
their  specific  gravity,  and  fall  to  the  bottom  of  the 
liquid ;  and  the  strata  situated  above  the  level  of  the 
cold  body  are  not  cooled  by  it  immediately. 

It  is  true  that  the  viscosity  of  liquids,  even  of  those 
which  possess  the  highest  known  degree  of  fluidity,  is 
still  much  too  great  to  allow  one  of  their  particles  indi- 
vidually being  moved  out  of  its  place  by  any  change  of 
specific  gravity  occasioned  by  heat  or  cold ;  yet  this  does 
not  prevent  currents  from  being  formed,  in  the  manner 
above  described,  by  small  masses  of  the  liquid  composed 
of  a  great  number  of  such  particles. 

The  existence  of  currents  in  the  ordinary  cases  of  the 
heating  and  cooling  of  liquids  cannot  any  longer  be  called 
in  question  ;  but  philosophers  are  not  yet  agreed  with 
respect  to  the  extent  of  the  effects  produced  by  those 
currents. 

In  treating  of  abstruse  subjects,  it  is  indispensably 
necessary  to  fix  with  precision  the  exact  meaning  of  the 
words  we  employ.  The  distinction  established  between 
conductors  and  non-conductors  of  heat  is  too  vague  not  to 
stand  in  need  of  explanation.  An  example  will  show 
the  ambiguity  of  these  expressions. 

If  two  equal  cubes  of  any  solid  matter,  —  copper,  for 
instance,  —  of  two  inches  in  diameter,  the  one  at  the  tem- 
perature of  60°,  the  other  at  100°,  be  placed  one  above 
the  other,-  the  cold  cube  will  be  heated  by  the  hot  one, 
and  this  last  will  be  cooled. 

If  the  cold  cube  be  placed  upon  a  table  and  its  upper 
surface  covered  by  a  large  plate  of  metal,  —  of  silver,  for 


276  Inquiries  concerning  the  Mode  of  the 

instance,  —  a  quarter  of  an  inch  thick,  and  if  the  hot  cube 
be  placed  upon  this  plate  immediately  above  the  cold 
cube,  the  heat  will  descend  through  the  metallic  plate  with 
a  certain  degree  of  facility,  and  will  heat  the  cold  cube. 

If  a  dry  board  of  the  same  thickness  with  the  metallic 
plate  be  substituted  in  its  place,  the  heat  will  descend 
through  the  wood,  but  with  much  less  celerity  than 
through  the  plate  of  silver. 

But  if  a  stratum  of  water  or  of  any  other  liquid  be  sub- 
stituted in  place  of  the  metallic  plate  or  of  the  board, 
the  result  will  be  very  different.  If,  for  instance,  the  cold 
cube  being  placed  in  a  large  tub  resting  on  the  middle 
of  its  bottom,  the  hot  cube  be  suspended  over  it  by 
cords,  or  in  any  other  manner  so  that  the  lower  surface 
of  the  hot  cube  be  immediately  above  the  upper  surface 
of  the  cold  cube,  at  the  distance  of  a  quarter  of  an  inch, 
and  the  tub  be  then  filled  with  water  at  the  same  tem- 
perature as  that  of  the  cold  cube,  the  heat  will  not 
descend  from  the  hot  cube  to  the  cold  one  through  the 
stratum  of  water  of  a  quarter  of  an  inch  in  thickness  that 
separates  them. 

We  may  with  propriety  call  silver  a  good  conductor  of 
heat,  and  dry  wood  a  bad  conductor ;  but  what  shall  we 
say  of  water  ?  I  have  called  it  a  non-conductor  for  want 
of  a  more  suitable  term,  but  I  always  felt  that  that  word 
expresses  but  imperfectly  the  quality  that  was  meant  to 
be  designated. 

In  the  experiment  of  the  two  cubes  plunged  in  water, 
if  the  hot  cube  be  placed  below  and  the  cold  cube  above 
it,  the  heat  will  not  only  be  communicated  from  the  hot 
to  the  cold  cube,  but  it  will  pass  even  more  rapidly  than 
when  the  two  cubes  are  separated  by  a  plate  of  silver. 
But  in  this  case  it  is  evident  that  the  heat  is  transported 


Propagation  of  Heat  in  Liquids.  277 

by  the  ascending  currents  which  are  formed  in  the  liquid 
in  consequence  of  the  heat  which  it  receives  from  the 
hot  body. 

The  existence  of  these  currents  in  certain  cases  has 
been  known  a  long  time,  but  philosophers  have  not  been 
sufficiently  attentive  to  the  many  curious  phenomena 
that  depend  upon  them.  It  has  not  even  been  suspected 
with  what  extreme  slowness  heat  passes  in  fluids,  from 
particle  to  particle,  de  proche  en  proche,  in  cases  where 
the  effects  of  such  communication  become  sensible. 

For  some  time  after  I  had  engaged  in  this  interesting 
inquiry,  I  conceived  that  this  kind  of  communication 
was  absolutely  impossible  in  all  cases  ;  but  a  more  atten- 
tive examination  of  the  phenomena  has  convinced  me 
that  this  conclusion  was  too  hasty.  As  early  as  the  be- 
ginning of  1800,  in  a  note  published  in  the  third  edition 
of  my  Seventh  Essay,  I  announced  a  conjecture  that  the 
non-conducting  power  of  fluids  might  perhaps  depend 
solely  on  the  extreme  mobility  of  their  particles ;  and  it 
is  certain,  if  this  conjecture  is  well  founded,  liquids  must 
necessarily  become  conductors  of  heat  (though  very  im- 
perfect ones)  in  all  cases  where  this  mobility  of  their 
particles  is  destroyed,  as  well  as  in  these  rare  but  yet 
possible  cases,  where  a  change  of  temperature  can  take 
place  in  a  liquid  without  giving  its  particles  any  ten- 
dency to  move,  or  to  be  moved  out  of  their  places. 

The  unequivocal  results  of  a  great  many  experiments 
have  shown,  that  in  ordinary  cases,  and  perhaps  in  all 
cases  where  heat  is  propagated  in  considerable  masses  of 
fluids,  its  distribution  is  accomplished  precisely  in  the 
manner  that  the  new  theory  supposes,  that  is  to  say,  by 
currents.  And  it  is  certain  that  the  knowledge  of  that 
fact  has  enabled  us  to  explain  in  a  satisfactory  manner 


278  Inquiries  concerning  the  Mode  of  the 

several  interesting  phenomena  of  nature,  which  before 
were  enveloped  in  much  obscurity. 

When  a  hot  solid  body  is  plunged  in  a  cold  liquid, 
there  can  be  no  doubt  concerning  the  existence  of  the 
vertical  ascending  currents  which  are  formed  in  the 
liquid,  and  which  convey  to  the  surface  the  heat  which 
its  particles  have  received ;  but  with  respect  to  the  strata 
of  liquid  situated  under  the  hot  body,  are  they  or  are  they 
not  heated  by  this  body  by  means  of  a  direct  communication  of 
heat  from  above  downwards^  from  f  article  to  particle,,  these 
particles  remaining  in  their  places?  This  is  a  question  on 
which  philosophers  are  not  yet  agreed.  As  it  is  a  ques- 
tion of  great  importance,  I  have  long  meditated  on  the 
means  of  deciding  it ;  and  after  several  unsuccessful 
attempts,  I  have  at  last  succeeded  in  making  an  experi- 
ment which  I  think  is  decisive. 

As  the  apparatus  which  I  used  for  this  experiment, 
and  which  I  have  the  honour  of  laying  before  the  assem- 
bly, is  somewhat  complicated  ;  and  as  it  is  indispensably 
necessary  to  be  intimately  acquainted  with  it,  in  order  to 
form  a  judgment  concerning  the  degree  of  confidence 
which  the  results  of  the  experiment  may  deserve,  —  it  is 
necessary  to  give  a  detailed  description  of  this  machinery. 
The  annexed  figure  gives  a  distinct  representation  of  its 
principal  parts.  It  is  drawn  on  a  scale  of  a  quarter  of 
an  inch  to  the  inch,  English  measure. 

A  B  (Plate  VII.)  is  a  board,  of  oak,  seen  in  profile; 
it  is  ii  inches  thick,  18  inches  long,  and  n  inches 
in  breadth.  It  serves  to  support  two  square  upright 
pillars,  C  C,  i8J  inches  in  height  and  i|  inches  square. 
They  are  firmly  fixed  in  the  board  at  the  distance  of  1 1 
inches  asunder,  and  serve  to  support  the  two  cross- 
pieces,  D  E,  F  G,  at  different  heights. 


Propagation  of  Heat  in  Liquids.  279 

These  cross-pieces  are  each  pierced  with  two  square 
holes,  at  the  distance  of  1 1  inches  one  from  the  other, 
into  which  the  upright  pillars  C  C  enter,  and  the  cross- 
pieces  are  supported  at  any  height  that  is  required,  by 
means  of  a  screw  of  compression.  These  screws  are 
represented  in  the  figure. 

The  cross-piece  F  G,  which  is  represented  in  pro- 
file, is  17  inches  in  length,  and  i|  inches  thick,  and  3 
inches  in  breadth.  It  is  pierced  in  the  middle  by  a 
cylindrical  hole  of  2  inches  in  diameter. 

The  cross-piece  D  E  is  17  inches  in  length  by  ij 
inches  in  thickness.  It  is  3  inches  wide  at  each  end  and 
6  inches  in  the  middle,  where  it  is  pierced  by  a  circular 
hole  5  inches  in  diameter. 

The  cross-piece  D  E  serves  to  support  the  annular 
vessel  H  I,  of  which  a  vertical  section  passing  through 
its  axis  is  seen  in  the  figure.  This  vessel,  formed  of 
thin  brass  plates,  is  5  inches  in  diameter  without,  3 
inches  in  diameter  within,  and  27^  inches  in  depth. 
This  vessel  is  filled  with  water  during  the  experiments 
to  the  height  of  2  J  inches ;  and  its  form  is  such,  that,  if 
the  water  that  it  contains  were  frozen  into  a  solid  mass 
of  ice,  this  piece  of  ice  would  have  the  form  of  a  tube 
or  perforated  cylinder  of  i  inch  in  thickness  and  2|- 
inches  high  by  5  inches  in  diameter  without.  Its  cylin- 
drical cavity  would  be  precisely  3  inches  in  diameter. 

K  L  is  a  vertical  and  central  section  of  a  cylindrical 
vessel  of  tin  of  10  inches  in  diameter  by  4^-  inches  in 
depth.  It  is  filled  with  water  to  the  height  of  4  inches, 
as  it  is  seen  in  the  figure. 

The  cross-piece  D  E  is  placed  at  such  a  height  that 
the  bottom  of  the  annular  vessel  H  I  is  plunged  a 
quarter  of  an  inch  under  the  surface  of  the  water  con- 
tained in  the  great  cylindrical  vessel  K  L. 


280  Inquiries  concerning  the  Mode  of  the 

In  the  axis  of  this  last  vessel  is  placed  a  small  hemi- 
spherical cup  of  wood  2  inches  in  diameter  without  and 
|-  of  an  inch  thick.  It  is  kept  in  its  place  by  a  short 
vertical  tube  of  tin,  soldered  to  the  bottom  of  the  cylin- 
drical vessel  K  L,  into  which  the  stalk  of  the  cup  fits 
tightly. 

The  middle  of  the  cavity  of  this  cup  is  occupied  by 
the  bulb  of  a  small  mercurial  thermometer  of  great  sen- 
sibility. Its  tube,  which  has  an  ivory  scale,  is  laid  down 
horizontally,  and  fixed  in  one  side  of  the  cup,  through 
which  the  tube  passes,  in  such  a  manner  that  the  lowest 
part  of  the  bulb  is  elevated  ^  of  an  inch  above  the 
bottom  of  the  cup.  The  diameter  of  the  bulb  being 
T37  of  an  inch,  and  the  hemispherical  cup  having  %  inch  of 
radius  within,  it  is  evident  that  the  upper  part  of  the 
bulb  is  j1^- of  an  inch  below  the  level  of  the  brim  of  the 
cup  that  contains  it.  To  avoid  charging  the  figure  with 
too  many  details,  the  scale  of  the  thermometer  is  not 
drawn,  but  the  tube  is  distinctly  represented. 

The  horizontal  cross-piece  F  G  serves  to  support  a 
very  essential  part  of  the  apparatus,  which  remains  to  be 
described. 

This  cross-piece  supports,  in  the  first  place,  a  vertical 
tube  of  wood,  M,  6T%  inches  in  length  and  2  inches  in 
diameter  without.  Its  interior  diameter  is  i^  inch. 
This  tube  is  supported  by  a  projecting  collar  (repre- 
sented in  the  figure),  2-|  inches  in  diameter,  which  rests 
on  the  cross-piece  F  G.  It  is  a  vertical  and  central  sec- 
tion of  this  tube  that  is  represented  in  the  figure,  and  it 
is  dotted  in  order  to  distinguish  it  from  the  surrounding 
parts  of  the  apparatus. 

The  lower  part  of  this  tube  is  plunged  T67  of  an  inch 
under  the  surface  of  the  water  in  the  large  cylindrical 


Propagation  of  Heat  in  L iquids.  2  8 1 

vessel  K  L  ;  and  it  is  placed  precisely  above  the  wooden 
cup  in  the  prolongation  of  its  axis,  the  lower  extremity 
of  the  tube  being  at  the  distance  of  ^  of  an  inch  above 
the  horizontal  level  of  the  brim  of  the  cup. 

On  the  top  of  the  tube  of  wood  is  placed  a  cylindrical 
vessel  N  O,  of  sheet  brass,  3  inches  in  diameter,  2} 
inches  high,  which  has  a  lateral  spout,  P  Q,  placed  a 
little  above  the  level  of  its  bottom. 

From  the  middle  of  the  bottom  of  this  vessel,  there 
descends  a  cylindrical  tube  of  brass,  6  inches  in  length 
and  i  inch  in  diameter,  which  ends  below  in  a  hollow 
conical  point,  as  represented  in  the  figure. 

R  S  is  a  vertical  and  central  section  of  a  funnel  of 
brass,  which  ends  below  in  a  cylindrical  tube  of  T3g-  of  an 
inch  in  diameter  and  6T6-g-  inches  long.  This  funnel  is 
kept  in  its  place  in  the  axis  of  the  cylindrical  vessel 
N  O  by  the  exact  fitting  of  its  upper  edge  upon  that 
of  the  vessel  into  which  it  is  adjusted. 

The  lower  end  of  the  tube  of  this  funnel  is  surrounded 
by  a  projecting  edge  or  flange  in  the  form  of  a  hollow 
inverted  cone.  The  diameter  of  this  conical  projecting 
brim  above,  at  its  base,  is  ^  of  an  inch,  and  it  is  sol- 
dered below  to  the  end  of  the  tube. 

When  hot  water  is  poured  into  the  funnel,  this  liquid, 
descending  by  the  tube  of  the  funnel,  strikes  against 
the  inner  surface  of  the  hollow  inverted  cone  which  ter- 
minates the  vertical  tube  that  belongs  to  the  vessel 
N  O,  and  then,  rising  up  through  this  last  tube  into  that 
vessel,  it  runs  off  by  its  spout.  It  was  with  a  view  to 
force  this  water  to  come  into  more  intimate  contact  with 
the  hollow  cone  that  the  projecting  edge,  in  form  of  an 
inverted  cone,  was  added  to  the  lower  end  of  the  tube  of 
the  funnel. 


282  Inquiries  concerning  the  Mode  of  the 

The  object  chiefly  in  view  in  the  arrangement  of  this 
apparatus  was  to  give  to  the  conical  point  which  termi- 
nates the  vertical  tube  of  the  vessel  N  O,  an  elevated 
temperature,  which  should  remain  constant  during  some 
time,  for  the  purpose  of  observing  if  the  heat,  which 
must  necessarily  be  communicated  by  this  metallic  point 
to  the  small  quantity  of  water  with  which  it  is  in  con- 
tact, and  which  is  confined  in  the  lower  part  of  the 
wooden  tube  M,  would  descend,  or  not,  to  the  ther- 
mometer which  was  placed  in  the  wooden  cup. 

There  was  still  one  source  of  error  and  uncertainty 
against  which  it  was  necessary  to  guard.  The  heat 
communicated  through  the  sides  of  the  wooden  tube  to 
the  water  contained  in  the  great  cylindrical  vessel  K  L 
might  be  transported  to  the  sides  of  that  vessel,  and, 
being  then  communicated  from  above  downwards 
through  these  sides,  might  heat  successively  the  lower 
strata  of  the  liquid,  and  at  last  that  stratum  in  which  the 
thermometer  was. 

It  was  to  prevent  this  that  the  annular  vessel  H  I  was 
used,  and  it  performed  its  office  in  the  following  man- 
ner: The  particles  of  water  contained  in  the  great  vessel 
K  L,  which,  being  in  contact  with  the  exterior  surface  of 
the  wooden  tube,  were  heated  by  that  tube,  could  not  fail 
to  rise  to  the  surface,  and  there  they  'necessarily  came 
into  contact  with  the  interior  sides  of  the  annular  vessel, 
to  which  they  communicated  the  excess  of  heat  they  had 
received  from  the  wooden  tube. 

This  heat,  passing  readily  through  the  thin  metallic 
sides  of  that  vessel,  was  given  off  as  fast  as  it  was  re- 
ceived to  the  particles  of  cold  water  contained  in  the 
vessel  which  were  in  contact  with  its  sides,  and  these 
particles,  rising  to  the  surface  of  the  water  con- 


Propagation  of  Heat  in  Liquids.  283 

tained  in  the  annular  vessel  in  consequence  of  their 
acquired  heat  and  levity,  the  progress  of  the  heat  from 
the  wooden  tube  to  the  sides  of  the  large  vessel  K  L, 
was  interrupted,  and  all  the  heat  that  passed  through  the 
sides  of  the  wooden  tube  was  by  these  means  turned  aside 
in  such  a  manner  that  it  could  no  longer  disturb  the 
progress  of  the  experiment,  nor  affect  the  certainty  of  its 
results. 

Before  I  proceed  to  give  an  account  of  the  result  of 
this  inquiry,  I  shall  take  the  liberty  to  recall  the  atten- 
tion of  the  Assembly  to  the  most  important  circum- 
stances of  the  experiment. 

On  pouring  boiling  water  in  a  small  uninterrupted 
stream  into  the  funnel,  the  hollow  conical  point  which 
terminates  the  vertical  tube  belonging  to  the  vessel  N  O 
was  heated,  and  kept  at  a  constant  temperature  little 
under  that  of  boiling  water. 

This  point  was  surrounded  by  a  small  quantity  of 
water  contained  in  the  cavity  of  the  lower  part  of  the 
wooden  tube,  and  as  this  water  could  not  change  its 
place  nor  be  displaced  by  the  surrounding  cold  water, 
being  enclosed  and  protected  by  the  sides  of  the  wooden 
tube,  it  would  necessarily  become  very  hot  in  a  short 
time. 

But  this  small  quantity  of  hot  water  lay  immedi- 
ately upon  a  stratum  of  cold  water,  which  separated  it 
from  the  bulb  of  the  thermometer,  placed  directly  under 
it  at  the  distance  of  only  half  an  inch. 

If  heat  could  pass  in  the  water  from  above  downwards, 
it  would  no  doubt  pass  from  the  lower  stratum  of  hot 
water  contained  in  the  open  end  of  the  wooden  tube  to 
the  bulb  of  the  thermometer,  which  lay  immediately 
below  it  and  at  so  small  a  distance. 


284  Inquiries  concerning  the  Mode  of  the 

Three  experiments  were  made  with  this  apparatus, 
and  always  with  exactly  the  same  results.  In  the  first, 
a  stream  of  boiling  water  was  poured  into  the  funnel 
during  10  minutes  ;  in  the  second,  during  12  minutes; 
and  in  the  third,  during  15  minutes. 

The  thermometer,  whose  bulb  was  in  the  wooden  cup, 
remained  at  perfect  rest  from  the  beginning  of  the  experi- 
ment to  the  end  of  it  without  showing  the  slightest  sign 
of  being  in  any  way  affected  by  the  hot  water  which  was 
so  near  it. 

These  experiments  were  made  at  Munich  in  the  month 
of  July,  1805  ;  the  temperature  of  the  air  and  of  the 
water  contained  in  the  vessel  K  L  being  70°  Fahrenheit. 

A  small  thermometer  placed  in  the  water  contained  in 
the  annular  vessel  H  I,  in  such  a  manner  that  its  bulb 
was  scarcely  submerged,  marked  that  this  water  had 
received  a  little  heat  in  each  of  the  three  experiments. 

Another  similar  thermometer  placed  in  the  water  con- 
tained in  the  large  vessel  K  L,  immediately  under  its 
surface  and  near  one  side  of  the  vessel,  showed  that  this 
water  had  not  acquired  any  sensible  increase  of  temper- 
ature during  the  experiments. 

From  the  results  of  these  experiments  we  are  au- 
thorized to  conclude,  that  heat  does  not  descend  in 
water  to  a  sensible  distance,  in  cases  where  the  particles 
of  the  liquid  which  receive  heat  are  exposed  to  be  dis- 
placed and  forced  upwards  by  the  surrounding  colder 
and  denser  particles,  that  is  to  say,  in  all  the  cases  (and 
they  are  the  most  common)  where  heat  is  applied  to  the 
strata  of  the  liquid  situated  under  its  surface. 

But  the  results  of  the  experiments  in  question  do  not 
prove  that  heat  cannot  in  any  case  descend  in  water;  and 
still  less  can  it  be  inferred  from  them,  that  all  direct  com- 


Propagation  of  Heat  in  Liquids.  285 

munication  of  heat  in  this  liquid,  from  particle  to  par- 
ticle, de  proche  en  proche,  is  impossible.  They  do  not 
even  prove  that  heat  did  not  descend,  to  a  small  distance^ 
below  the  level  of  the  end  of  the  wooden  tube  in  these 
experiments ;  for  it  is  certain  that  that  event  could  take 
place  without  the  thermometer,  which  was  situated  a 
little  lower,  being  in  any  way  affected  by  that  heat. 

The  particles  of  water  situated  at  a  very  small  distance 
below  the  level  of  the  lower  end  of  the  wooden  tube, 
being  heated  by  the  stratum  of  hot  water  which  rested 
immediately  on  them,  might  have  been  displaced  by  the 
surrounding  colder  and  denser  particles,  and  forced  to 
rise  to  the  surface ;  and  these  last  being  in  their  turn 
heated,  forced  upwards  and  replaced  by  other  cold  par- 
ticles, it  is  evident  that  the  heat  could  not  make  its 
way  downwards  so  far  as  to  arrive  at  the  thermometer 
through  a  stratum  of  liquid,  which,  though  apparently 
at  rest,  was  nevertheless  in  part  composed  of  particles 
which  were  continually  changing. 

I  have  long  suspected  that  the  apparent  impossibility 
of  a  direct  communication  of  heat  between  neighbouring 
particles  of  fluids  depends  solely  on  the  great  mobility 
of  those  particles  (see  note,  p.  202,  Vol.  II.  of  my 
Essays,  jd  edition,  London,  1800);  and  if  this  sus- 
picion be  well  founded,  it  is  certain  that  when  this 
mobility  ceases,  the  effect  which  depends  on  it  must 
cease  likewise. 

When  I  speak  of  the  mobility  of  the  particles  of  a 
liquid  amongst  each  other,  I  am  very  far,  as  I  have 
already  observed,  from  supposing  that  individually  they 
can  enjoy  a  free  motion.  I  was  formerly  of  that  opinion, 
but  a  more  attentive  investigation  of  the  phenomena  has 
convinced  me  that  I  was  mistaken.  But  although  one 


286          Inquiries  concerning  the  Mode  of  the 

individual  particle  of  a  liquid  can  never  be  put  in  mo- 
tion in  consequence  of  a  change  of  its  specific  gravity 
occasioned  by  a  change  of  temperature,  yet  what  cannot 
happen  to  a  single  particle  may  easily  and  must  neces- 
sarily happen  to  small  masses  of  the  liquid  consisting 
of  a  great  number  of  these  particles  united,  as  is  abun- 
dantly proved  by  the  currents  which  are  so  easily  excited 
by  the  contact  of  a  hot  or  cold  body  plunged  in  a 
liquid. 

The  force  by  which  the  particles  of  liquids  adhere  to- 
gether is  very  great,  and  it  is  more  than  probable  that  it 
is  the  cause  of  many  very  interesting  phenomena,  and 
amongst  others  of  the  suspension  of  the  heavy  bodies 
which  much  lighter  liquids  so  frequently  hold  in  solu- 
tion. 

From  the  result  of  an  experiment  which  I  made  some 
years  ago  in  order  to  determine  the  measure  of  the  vis- 
cosity or  the  want  of  perfect  fluidity  in  water  at  the  tem- 
perature of  64°  F.,  I  found  reason  to  conclude  that  a 
solid  body,  having  a  surface  equal  to  368  square  inches, 
which  should  weigh  only  one  grain  Troy  more  than  an 
equal  volume  of  water,  would  remain  suspended  in  that 
liquid ;  and  from  this  datum  it  is  easy  to  find  by  calcu- 
lation what  ought  to  be  the  diameter  of  a  small  solid 
spherule  of  the  heaviest  matter,  —  of  gold,  for  instance, 
—  in  order  to  its  remaining  suspended  in  water  in  con- 
sequence of  the  viscosity  of  that  liquid. 

Having  made  this  calculation  in  order  to  satisfy  my 
curiosity,  I  found  that  a  solid  spherule  of  pure  gold,  of 
the  diameter  of  ^"oWir  (or  exactly  ^-g-grT^)  °f  an  incn> 
ought  to  remain  suspended  in  water  in  consequence  of 
the  adhesion  of  the  particles  of  that  liquid  to  each  other. 
But  I  shall  return  to  this  subject  on  a  future  occasion. 


Propagation  of  Heat  in  Liquids.  287 


[THE  preceding  paper  is  printed  from  Nicholson's  Journal,  XIV. 
(1806),  pp.  355-  363.  The  paper,  in  a  somewhat  modified  form,  ap- 
pears in  the  Bibliotheque  Britannique  (Science  et  Arts),  XXXII.  ( 1 806), 
pp.  123-141,  to  which  periodical  it  was  contributed  by  Count  Rum- 
ford  in  manuscript,  which  was  translated  by  the  French  editor.  In 
this  version  the  beginning  of  the  paper  is  much  abridged  ;  but  in  the 
latter  part  Rumford  elaborated  his  speculations  in  regard  to  the  effects 
produced  by  viscosity  on  the  propagation  of  heat  in  liquids  more  at 
length  than  in  Nicholson's  Journal.  In  order  to  give  fully  his  views 
on  the  subject,  this  portion  of  the  French  paper  is  here  appended. 

"  If  there  is  no  direct  communication  of  heat  between  contiguous  par- 
ticles of  water  at  different  temperatures,  then  the  apparent  mean  tem- 
perature, which  results  so  quickly  when  cold  water  is  poured  into  a 
mass  of  warm  water,  must  be  produced  by  currents  caused  by  differ- 
ences in  the  specific  gravity  of  the  masses  of  the  liquid  at  different  tem- 
peratures. And  if  it  is  asked  why  the  hot  and  cold  particles,  thus  mixed 
together,  do  not  separate  again,  on  account  of  the  difference  in  their 
specific  gravity,  we  must  seek  for  the  reason  in  the  imperfect  fluidity  of 
the  water.  This  cause  may  keep  the  particles  of  water  suspended,  out 
of  their  natural  position,  just  as  it  keeps  in  suspension,  as  well  in  other 
liquids  as  in  water,  particles  of  foreign  substances,  which,  although 
specifically  heavier  or  specifically  lighter  than  the  medium,  are  so  small 
that  the  amount  by  which  they  are  heavier  or  lighter  than  the  surround- 
ing liquid  is  not  sufficient  to  overcome  its  viscosity. 

"  This  want  of  perfect  fluidity,  a  condition  common  to  all  liquids"  in 
different  degrees,  gives  rise  to  a  great  number  of  very  interesting  phe- 
nomena, and  it  is  a  subject  worthy  of  the  close  attention  of  philosophers. 

"  From  the  result  of  an  experiment  which  I  made  a  long  time  ago  in 
order  to  determine  the  measure  of  the  viscosity  of  pure  water  at  the 
temperature  of  64°  F.,  that  is  the  force  necessary  to  separate  contigu- 
ous particles  of  that  liquid,  I  found  reason  to  conclude  that  a  solid  body, 
having  a  surface  equal  to  368  square  inches,  which  should  weigh  only 
one  grain  Troy  more  than  an  equal  volume  of  water,  would  remain  sus- 
pended in  that  liquid  ;  and  from  this  datum  it  is  easy  to  find,  by  calcu- 
lation, what  ought  to  be  the  diameter  of  a  small  solid  spherule  of  the 
heaviest  matter,  —  of  gold,  for  instance,  —  in  order  to  its  remaining 
suspended  in  water  in  consequence  of  the  viscosity  of  that  liquid :  and 


288  Inquiries  concerning  the  Mode  of  the 

it  is  also  easy  to  prove,  from  the  inflection  which  light  experiences  in 
passing  over  the  surface  of  an  opaque  solid  body,  that  a  considerable 
quantity  of  opaque  solid  matter  could  be  held  suspended  in  water 
without  sensibly  diminishing  its  transparency,  and  without  changing  its 
colour;  that  is  to  say,  without  giving  any  indication  of  its  presence.* 

"I  have  long  suspected  that  the  suspension  of  solid  substances  which 
are  held  in  solution  by  liquids  is  due  solely  to  the  imperfect  fluidity  of 
the  solvents,  and  the  results  of  a  great  number  of  experiments  which  I 
have  made  to  elucidate  this  important  subject  have  always  confirmed 
this  opinion.  Since,  then,  bodies  specifically  heavier  than  water  can 
nevertheless  remain  suspended  in  that  liquid,  there  can  be  no  difficulty 
in  admitting  that  isolated  particles  of  cold  water  can  equally  remain 
motionless  in  the  warm  water  with  which  they  find  themselves  acci- 
dentally mixed.  But  although  this  may  be  true  of  the  individual  par- 
ticles, the  same  principle  cannot  apply  to  masses  of  sensible  size  made 
up  of  a  great  number  of  these  particles.  These  masses  must  yield  to 
the  natural  effect  of  the  differences  in  their  specific  gravity,  and  form 
currents  which  will  be  ascending  or  descending  according  as  the  masses 
in  question  are  warmer  or  colder  than  the  surrounding  liquid  ;  and 
these  currents  must  contribute  very  largely  to  the  intimate  mixture  of 
the  particles  at  different  temperatures,  and  must  soon  bring  about  a  cer- 
tain uniform  temperature  throughout  the  entire  mass  of  the  liquid. 

"  I  said  this  uniformity  of  temperature  may  be  only  apparent ;  because, 
if  water  is  really  a  perfect  non-conductor  of  heat,  the  particles  of  cold 
water,  at  least  those  which  have  not  been  warmed  by  contact  with  the 
walls  of  the  vessel  in  which  they  are  contained,  ought  to  remain  cold 
in  spite  of  their  more  or  less  intimate  mixture  with  the  warm  particles; 
but,  notwithstanding  this  fact,  the  mean  temperature  of  the  liquid,  as 
shown  by  the  thermometer,  will  be  precisely  the  same  as  if  there  had 
been  an  actual  communication  of  heat  among  the  particles. 

"  Long  after  I  had  had  reason  to  persuade  myself  that  all  the  heat  ac- 
quired by  liquids,  when  they  are  warmed,  is  communicated  by  the  ves- 
sel containing  them  to  the  individual  particles,  which  are  successively 

*  In  order  to  satisfy  my  curiosity,  I  found,  by  calculation,  the  diameter  which  a 
small  solid  spherule  of  gold  ought  to  have  in  order  to  its  remaining  suspended  in 
water  in  consequence  of  the  viscosity  of  that  liquid.  I  found  this  diameter  to  be 
— ^ — ,  or,  in  round  numbers,  — —  of  an  inch ;  that  is  to  say,  about  two  hundred 
times  smaller  than  the  diameter  of  a  single  fibre  of  raw  silk,  as  spun  by  the  worm, — 
an  object  which  is  so  fine  as  scarcely  to  be  visible. 


Propagation  of  Heal  in  Liquids.  289 

brought  into  contact  with  its  sides  by  the  currents  formed  in  the  mass 
of  the  liquid,  —  a  long  time,  I  say,  after  I  had  adopted  this  opinion,  I 
continued  to  doubt  whether  single  particles  of  warm  water,  when  com- 
pletely surrounded  by  particles  of  cold  water,  and  remaining  undis- 
turbed in  the  midst  of  them,  might  not  be  able  to  communicate  to 
these  neighbouring  particles  that  excess  of  heat  which  the  shortness  of 
the  time  of  contact  when  the  particles  are  in  motion  does  not  allow 
them  to  impart  to  each  other.  Indeed,  if  the  property  of  water  by 
which  it  is  an  apparent  non-conductor  of  heat  depends  solely  upon 
the  extreme  mobility  of  its  particles,  it  is  evident  that  the  communica- 
tion of  heat,  under  the  circumstances  just  supposed,  must  necessarily 
take  place ;  and  it  must  be  remembered  that  in  this  case  the  fluidity  of 
the  liquid,  as  far  as  the  particles  in  question  are  concerned,  is  as  truly 
destroyed  as  if  the  entire  mass  were  converted  into  ice. 

"The  inquiry  as  to  the  non-conducting  power  of  fluids  —  an  inquiry  to 
which  my  experiments  and  observations  have  given  rise  —  is,  no  doubt, 
of  great  interest  to  science ;  and,  whatever  may  be  the  final  result  of 
its  investigation,  I  shall  regard  myself  fortunate  in  having  drawn  the 
attention  of  a  great  number  of  enlightened  philosophers  towards  an 
object  which  was  long  neglected,  and  which  was  so  worthy  of  being 
studied."] 


»9 


EXPERIMENTS    AND    OBSERVATIONS 


ADHESION    OF   THE    PARTICLES   OF   WATER   TO 
EACH    OTHER. 

WE  often  see  small  bodies  of  a  specific  gravity 
much  exceeding  that  of  water  float  upon  the 
surface  of  that  fluid.  Such,  for  example,  are  very  small 
grains  of  sand,  fine  filings  of  the  metals,  and  even  small 
sewing-needles. 

So  extraordinary  a  phenomenon  has  not  failed  to 
excite  the  attention  of  philosophers.  It  formed  a  sub- 
ject of  discussion  at  the  last  sitting  of  the  Class,  and  as 
this  remarkable  fact  is  intimately  connected  with  a  sub- 
ject of  research  upon  which  I  have  been  long  employed, 
I  shall  here  give  an  account  of  some  experiments  I  have 
made  to  elucidate  the  same,  which  have  afforded  results 
of  considerable  interest. 

Suspecting  that  the  presence  of  air  adhering  to  these 
small  floating  bodies,  which  is  generally  considered  as 
the  cause  of  their  supension,  is  not  indispensably  neces- 
sary for  the  success  of  the  experiment,  I  made  the  fol- 
lowing experiments. 

Experiment  No.  i.  —  Having  half  filled  with  water  a 
wine-glass  one  inch  and  a  half  in  diameter  at  its  edge, 
I  poured  on  the  surface  of  the  water  a  stratum  of  sul- 
phuric ether,  one  inch  and  a  half  in  thickness ;  and 
when  the  whole  was  perfectly  still,  I  took  a  very  small 


On  the  Adhesion  of  the  Particles  of  Water,  etc.    291 

sewing-needle  with  a  pair  of  pincers,  which  I  introduced 
below  the  ether,  where,  holding  it  horizontally  at  a  small 
distance  from  the  surface  of  the  water,  I  let  it  fall.  The 
needle  descended  to  the  water,  and  there  floated  on  its 
surface. 

Experiment  No.  2.  —  Having  melted  some  tin,  I  poured 
it  into  a  spherical  wooden  box,  and,  shaking  it  strongly, 
the  metal  in  cooling  was  reduced  to  powder,  which  was 
then  sifted. 

On  examining  this  powder  with  a  magnifier,  it  ap- 
peared composed  of  small  spherules  of  different  sizes ; 
but  these  spherules  were  too  small  to  be  distinguished 
by  the  naked  eye. 

I  took  up  on  the  point  of  a  spatula  a  very  small 
quantity  of  this  metallic  powder,  and  poured  it  gently 
from  the  height  of  a  quarter  of  an  inch  on  to  the  surface 
of  the  ether  which  rested  upon  the  water  in  the  glass. 

The  powder  descended  wholly  through  the  ether,  and 
when  it  arrived  at  the  surface  of  the  water,  it  remained 
floating. 

Experiment  No.  3.  —  Having  poured  a  large  drop  of 
mercury  into  a  china  plate,  I  broke  it  into  a  great  num- 
ber of  small  spherules. 

In  order  to  take  up  and  convey  these  small  spherules 
one  by  one,  I  made  a  small  tool  or  shovel  out  of  a  piece 
of  brass  wire,  five  inches  long,  and  about  one  twentieth 
of  an  inch  in  diameter,  bent  to  a  right  angle  at  one 
of  its  extremities.  This  bent  part  was  about  a  quar- 
ter of  an  inch  long,  and  was  hammered  flat,  sharpened, 
and  made  a  little  concave. 

By  means  of  this  tool  I  took  up  a  small  spherule  of 
mercury,  about  one  sixtieth  of  an  inch  in  diameter,  which 
I  carefully  conveyed  into  the  stratum  of  ether  to  the 


29 2  On  the  Adhesion  of  the  Particles 

distance  of  about  one  twentieth  of  an  inch  from  the  sur- 
face of  the  water  beneath ;  and  there,  by  a  little  inclina- 
tion of  the  instrument,  I  caused  the  spherule  of  mercury 
to  roll  gently  on  to  the  surface  of  the  water. 

The  spherule  descended  to  that  surface,  and  there  re- 
mained floating. 

When  the  eye  was  placed  lower  than  the  surface  of 
the  water,  and  the  spherule  was  observed  by  looking  up- 
wards through  the  glass,  it  appeared  suspended  in  a  kind 
of  bag,  a  little  below  the  level  of  the  surface. 

Having  placed  a  second  spherule  of  mercury  on  the 
surface  of  the  water,  it  immediately  moved  towards  the 
former,  and,  approaching  it  with  an  accelerated  motion, 
fell  down  into  the  same  cavity,  which  then  became  lon- 
ger ;  but  the  two  spherules  did  not  unite. 

Having  placed  a  third  spherule  on  the  surface  of  the 
water,  it  joined  the  two  others;  but  the  weight  of  these 
three  spherules  together  being  too  great  to  be  supported 
by  the  kind  of  pellicle  which  is  formed  at  the  surface  of 
the  water,  the  bag  was  broken,  and  the  spherules  de- 
scended through  the  water  to  the  bottom  of  the  vessel. 

When  the  experiment  was  made  with  a  spherule  of 
mercury  a  little  larger,  namely,  about  the  fortieth  or  fif- 
tieth of  an  inch,  it  never  failed  to  break  the  pellicle  of 
the  water,  and  to  descend  through  that  liquid  to  the 
bottom  of  the  glass.  But  when  the  viscidity  of  the 
water  was  increased  by  dissolving  a  small  quantity  of 
gum-arabic  in  it,  still  larger  spherules  of  mercury  were 
supported  at  the  surface  of  the  liquid. 

A  spherule  of  mercury  of  a  proper  size  to  be  sup- 
ported by  water  at  its  surface,  if  placed  gently  there, 
would  not  fail  to  make  its  way  through  the  pellicle  of 
the  water,  if  let  fall  from  too  great  an  height. 


of  Water  to  each  other.  293 

All  the  preceding  experiments  were  repeated  with 
a  stratum  of  essential  oil  of  turpentine,  and  afterwards 
with  one  of  oil  of  olives,  placed  on  the  water  contained 
in  the  glass  instead  of  the  ether,  and  the  results  were 
in  all  respects  similar.  I  thought,  however,  that  the 
spherules  of  mercury  which  were  suspended  upon  the 
water  were  rather  larger  when  the  surface  of  the  water 
was  covered  with  oil  than  with  ether;  and  in  the  ex- 
periments made  with  the  powder  of  tin  poured  on  the 
oil,  the  finest  parts  of  the  powder  in  very  small  quan- 
tity floated  on  the  surface  of  the  oil. 

Experiment  No.  4.  —  Having  found  means  to  place  a 
stratum  of  alcohol  on  the  water  contained  in  the  glass, 
so  that  the  two  liquids  appeared  as  distinct  from  each 
other  as  when  the  upper  stratum  was  oil,  I  poured 
from  a  very  small  height  a  small  quantity  of  the  very 
fine  powder  of  tin  upon  the  alcohol. 

This  powder  totally  descended  through  the  alcohol 
and  the  water,  without  giving  the  smallest  indication  of 
its  having  been  subjected  to  any  resistance  at  the  sur- 
face of  the  latter  fluid. 

Though  this  last  surface  appeared  .very  distinctly  to 
the  eye,  yet,  judging  from  the  manner  in  which  the 
metallic  powder  descended  to  the  bottom  of  the  glass, 
I  am  disposed  to  think  that  it  had  no  existence ;  and,  in 
fact,  it  is  probable  that  it  was  destroyed  by  the  chemical 
action  of  the  alcohol  in  contact  with  the  water. 

In  order  to  examine  more  accurately  the  kind  of  film 
which  is  formed  at  the  surface  of  the  water,  I  made  the 
following  experiment. 

Experiment  No.  5.  —  In  a  cylindrical  glass  with  a  solid 
foot,  the  diameter  of  which  was  fourteen  lines,  or  about 
an  inch  and  a  half  English,  and  ten  inches  in  height,  I 


294  OH  t?ie  Adhesion  of  the  Particles 

poured  very  limpid  water  to  the  height  of  nine  inches, 
and  on  the  water  I  placed  a  stratum  of  ether,  three  lines 
or  twelfths  of  an  inch  in  thickness.  I  then  placed  on 
the  surface  of  the  water  a  number  of  small  solid  bodies, 
which  remained  suspended,  such  as  a  small  spherule  of 
mercury,  some  pieces  of  extremely  fine  silver  wire,  two 
or  three  lines  in  length,  and  a  little  of  the  powder  of 
tin.  When  the  whole  was  perfectly  tranquil,  I  took 
the  glass  in  both  hands,  and  carefully  raising  it,  I  turned 
it  three  or  four  times  round  its  axis  with  considerable 
rapidity,  keeping  it  in  a  vertical  position.  All  the  small 
bodies  suspended  at  the  surface  of  the  water  turned 
round  along  with  the  glass  and  stopped  when  it  was 
stopped ;  but  the  liquid  water  below  the  surface  did 
not  at  first  begin  to  turn  along  with  the  glass,  and  its 
motion  of  rotation  did  not  cease  all  at  once  upon  stop- 
ping that  of  the  vessel.  In  fact,  all  the  appearances 
showed  that  there  was  a  real  pellicle  at  the  surface  of  the 
water,  and  that  this  pellicle  was  strongly  attached  to  the 
sides  of  the  glass  so  as  to  move  along  with  it. 

Upon  examining  with  a  good  magnifier,  through  the 
stratum  of  ether,  the  small  bodies  which  were  supported 
at  the  surface  of  the  water,  the  existence  of  this  pellicle 
could  no  longer  be  doubted ;  more  particularly  when  it 
was  touched  with  the  point  of  a  needle.  For  in  this 
case  all  the  small  bodies  were  observed  to  tremble  at  the 
same  time. 

Having  left  this  small  apparatus  at  repose  in  a  quiet 
chamber  until  the  stratum  of  ether  was  entirely  evap- 
orated, I  examined  it  again  with  a  magnifier.  The  sur- 
face of  the  water  was  precisely  in  the  same  state ;  the 
small  solid  bodies  were  still  there,  in  the  same  situation, 
and  at  the  same  distances  from  each  other. 


of  Water  to  each  other.  295 

When  this  experiment  was  made  with  a  cylindrical 
glass  of  much  larger  diameter,  the  effects  of  the  adhesion 
of  the  pellicle  of  the  water  to  the  sides  of  the  vessel 
were  much  less  sensible  with  regard  to  those  parts  of 
the  same  which  were  situated  near  the  axis.  It  was  dif- 
ficult to  prevent  the  small  bodies  which  floated  on  the 
surface  of  the  water  from  uniting,  and  when  united  they 
often  formed  masses  too  heavy  to  continue  to  be  sup- 
ported; and,  having  broken  the  pellicle  of  the  water, 
they  fell  to  the  bottom  of  the  vessel. 

If  the  particles  of  water  adhere  strongly  to  each  other, 
it  appears  to  me  to  be  a  necessary  consequence  that  a 
kind  of  pellicle  will  be  formed  at  the  upper  surface  of 
the  liquid,  and  even  at  all  its  surfaces,  whatever  may  be 
in  other  respects  the  mobility  of  these  particles,  or  rather 
of  the  small  liquid  masses  composed  of  a  great  number 
of  them,  when  they  are  remote  from  the  surface  and 
possess  their  fluidity  without  impediment. 

When  a  small  solid  body,  placed  on  the  surface  of 
water,  becomes  wetted,  it  immediately  descends  beneath 
the  pellicle,  which  no  longer  opposes  its  resistance. 
At  this  period  the  viscidity  of  the  water  begins  to  mani- 
fest itself  in  a  very  different  manner,  but  with  infinitely 
less  effect  than  when  it  acts  at  the  confines  of  the 
liquid.  But  it  is  not  yet  time  to  inquire  into  this  part 
of  our  subject. 

With  a  view  to  render  sensible  the  resistance  which 
the  pellicle  of  the  inferior  surface  of  a  stratum  of  water 
opposes  to  a  solid  body  which  passes  through  that 
stratum  by  falling  freely  downwards,  I  made  the  follow- 
ing experiment. 

Experiment  No.  6.  —  Having  filled  a  small  wine-glass 
to  about  half  its  height  with  very  pure  mercury,  I 


296  On  the  Adhesion  of  the  Particles 

poured  a  stratum  of  water  of  three  lines  in  thickness 
upon  the  mercury,  and  upon  that  a  stratum  of  ether  of 
two  lines. 

When  the  whole  was  at  rest,  I  took  with  the  small 
tool  before  described  a  spherule  of  mercury  of  about  one 
third  of  a  line  in  diameter,  and  let  it  fall  through  the 
stratum  of  ether. 

This  spherule,  being  too  heavy  to  be  supported  by  the 
pellicle  at  the  superior  surface  of  the  water,  broke  it,  and 
descended  through  that  fluid ;  but  upon  its  arrival  at 
the  inferior  surface  it  was  stopped,  and  remained  there, 
preserving  its  spherical  form. 

I  moved  this  spherule  with  the  extremity  of  a  feather, 
and  even  compressed  it;  but  it  always  preserved  its 
form  without  mixing  with  the  mass  of  mercury  on  which 
it  appeared  to  rest. 

It  was  no  doubt  the  pellicle  of  the  inferior  surface  of 
the  stratum  of  water  which  prevented  this  contact,  and 
as  this  pellicle  was  supported  by  the  mercury  on  which 
it  rested,  I  was  not  at  all  surprised  to  find  that  it  could 
support,  without  being  broken,  a  spherule  of  mercury 
much  larger  than  the  pellicle  of  the  superior  surface 
could  support. 

In  order  to  satisfy  myself  that  the  viscidity  of  the 
water  was  the  cause  of  the  suspension  of  this  mercurial 
globule  at  the  bottom  of  that  fluid,  I  repeated  the  ex- 
periment and  varied  it  by  substituting  water  containing 
a  certain  quantity  of  gum-arabic,  in  solution,  in  the 
place  of  pure  water ;  and  I  found,  in  fact,  that  much 
larger  spherules  were  supported  when  the  viscidity  of 
the  water  was  thus  augmented. 

To  prove  this  fact  in  another  manner,  I  again  varied 
the  experiment,  by  placing  a  stratum  of  ether  im- 


of  Water  to  each  other.  297 

mediately  upon  the  mercury.  The  particles  of  this 
liquid  appear  to  have  very  little  adhesion  to  each  other; 
for  which  reason  I  imagined  that  the  kind  of  film  that 
would  be  formed  at  its  surface  must  have  very  little 
force.  The  results  of  my  experiment  fully  confirmed 
this  conjecture. 

The  very  smallest  spherules  of  mercury  which  I  let 
fall  through  this  liquid  seldom  failed  to  mix  immediately 
with  the  mass  of  mercury  on  arriving  at  its  surface, 
where  they  entirely  disappeared ;  and  I  have  never  suc- 
ceeded in  causing  either  a  spherule  of  mercury,  or  the 
smallest  metallic  particle,  or  any  other  body  of  greater 
specific  gravity  than  ether,  to  swim  upon  its  surface. 

The  results  of  the  experiment  were  not  perceptibly 
different  when  alcohol  was  substituted  in  the  place  of 
ether. 

It  is  known  that  ether  evaporates  very  rapidly.  Is 
not  this  another  proof  that  the  particles  of  this  liquid 
adhere  to  each  other  with  much  less  force  than  those  of 
water  ?  But  the  following  experiment  proves  this  fact 
in  a  decisive  manner. 

Experiment  No.  7.  —  Having  half  filled  a  small  cylin- 
drical glass  with  mercury,  I  placed  on  the  mercury  a 
stratum  of  ether  four  lines  in  thickness,  and  blew  upon 
the  ether  with  a  pair  of  common  bellows. 

In  less  than  one  minute  the  ether. had  disappeared. 

The  same  experiment  being  made  with  water,  no  sen- 
sible quantity  of  this  fluid  had  disappeared  in  one  min- 
ute. 

The  objects  which  are  before  our  eyes  from  the  earli- 
est periods  of  our  lives  seldom  employ  our  meditation, 
and  not  often  our  attention.  We  see,  without  sur- 
prise, immense  masses  of  dust  raised  by  the  winds  and 


298  On  the  Adhesion  of  the  Particles 

carried  to  great  distances ;  and  at  the  same  time  we 
know  that  every  particle  of  this  powder  is  really  a  stone, 
almost  three  times  as  heavy  as  water,  and  of  a  size  so 
considerable  that  its  form  may  be  perfectly  seen  by 
means  of  a  good  microscope. 

And  we  see  also,  without  surprise,  that  water,  which  is 
much  lighter  than  dust,  and  is  composed  of  particles  in- 
comparably smaller,  is  not  carried  off  by  the  wind  in 
the  same  manner. 

In  order  to  convince  ourselves  that  the  particles  of 
water  do  strongly  adhere  to  each  other,  and  that  they  re- 
quire to  do  so  in  order  to  prevent  the  greatest  confusion 
in  the  universe,  we  need  only  figure  to  ourselves  the  in- 
evitable consequences  that  would  result  from  the  want 
of  such  an  adhesion. 

The  particles  of  water  would  be  raised  and  carried  off 
by  the  winds  with  infinitely  more  facility  than  the  finest 
and  lightest  dust.  Every  strong  breeze  setting  in  from 
the  ocean  would  bring  with  it  a  great  inundation. 
Navigation  would  be  impossible,  and  the  banks  of  all 
the  seas,  lakes,  and  large  rivers  would  be  uninhabitable. 

The  adhesion  of  the  particles  of  water  to  each  other  is 
the  cause  of  the  preservation  of  that  liquid  in  masses. 
It  covers  the  surface  with  a  very  strong  pellicle,  which 
defends  and  prevents  it  from  being  dispersed  by  the 
winds.  Without  this  adhesion,  water  would  be  more 
volatile  than  ether,  and  more  fugitive  than  dust. 

But  the  adhesion  is  also  the  cause  of  other  phenom- 
ena, which  are  of  the  greatest  importance  in  the  phe- 
nomena of  nature. 

The  viscidity  which  results  from  the  mutual  adhesion 
of  the  particles  of  water  renders  this  fluid  proper  to 
hold  all  kinds  of  bodies  in  solution,  as  well  the  most 


of  Water  to  each  other.  299 

heavy  as  the  lightest,  provided  always  that  they  be  re- 
duced to  very  minute  particles. 

I  have  found,  by  a  calculation  founded  on  facts  which 
appear  to  me  to  be  decisive,  that  a  solid  spherule  of 
pure  gold,  of  the  diameter  of  s¥-oV<5T  °f  an  mcn> 
would  be  suspended  in  water  by  the  effect  of  its  viscid- 
ity, even  though  this  small  body  should  be  completely 
wetted  and  submerged  in  a  tranquil  mass  of  the  fluid. 

This  viscidity,  or  want  of  perfect  fluidity,  which 
causes  it  to  hold  every  kind  of  substance  in  solution, 
renders  it  eminently  proper  to  become  the  vehicle  of 
nourishment  to  plants  and  animals;  and  we  accordingly 
see  that  it  is  exclusively  employed  in  this  office. 

If  the  adhesion  of  the  particles  of  water  to  each  other 
were  to  cease,  and  the  fluidity  of  this  body  were  to 
become  perfect,  every  living  being  would  perish  by 
inanition. 

May  I  be  permitted  to  remark  the  simplicity  of  the 
means  employed  by  Nature  in  all  her  operations  ! 

May  I  be  permitted  to  express  my  profound  admira- 
tion and  adoration  of  the  Author  of  so  many  wonders ! 

[This  paper  is  printed  from  Nicholson's  Journal,  XV.  (1806), 
pp.  52-56,  157-159'  I73-I75-] 


CONTINUATION 

OF 

EXPERIMENTS  AND  OBSERVATIONS 

ON    THE 

ADHESION  OF  THE  PARTICLES  OF  LIQUIDS  TO 
EACH  OTHER. 

BEFORE  proceeding  with  the  account  of  my  ex- 
periments, I  shall  take  the  liberty  of  going  back 
to  a  distant  period,  and  of  describing  to  the  Class  an 
occurrence  which  first  fixed  my  attention  on  this  subject 
and  led  me  to  engage  in  these  researches. 

Being  occupied  in  the  year  1786  with  a  series  of 
experiments  on  the  oxygen  gas  which  is  disengaged  from 
water  when  this  liquid  mixed  with  various  solid  sub- 
stances is  exposed  to  the  action  of  the  sun's  rays,  among 
the  substances  employed  in  my  investigation  was  a 
quantity  of  raw  silk,  wound  from  the  cocoon  on  pur- 
pose for  this  experiment,  in  a  single  thread,  just  as  it  is 
produced  by  the  silkworm. 

It  being  necessary  for  completing  my  calculations  that 
I  should  determine  with  precision  the  amount  of  the 
surface  of  this  thread,  which  was  almost  two  leagues  in 
length,  and  which  weighed  in  the  air  only  about  20 
grains  Troy,  and  having  no  means  of  measuring  di- 
rectly the  exact  diameter  of  the  thread,  I  undertook  to 
calculate  it  from  the  known  length  of  the  thread  and 
the  specific  gravity  of  the  substance. 

It  was  in  weighing  this  substance  in  water  to  ascertain 
its  specific  gravity,  that  I  encountered  difficulties  which 


On  the  Adhesion  of  the  Particles  of  Liquids,  etc.     301 

for  a  long  time  seemed  to  me  insurmountable,  but  by 
the  exercise  of  patience  and  due  precaution,  I  succeeded, 
after  somewhat  long  and  difficult  labour,  in  accomplish- 
ing my  object. 

Those  who  are  in  the  habit  of  making  delicate  experi- 
ments with  the  hydrostatic  balance  will  conjecture  imme- 
diately, before  I  have  time  to  say  it,  that  it  was  the  air 
which  remained  obstinately  attached  to  the  surface  of 
the  silk  when  I  weighed  it  in  water,  which  rendered  this 
operation  so  difficult. 

I  do  not  wish  to  abuse  the  patience  of  the  Class  by 
giving  it  a  detailed  account  of  all  the  means  I  was  obliged 
to  try  before  finding  an  efficient  remedy  for  this  incon- 
venience ;  it  will  suffice  to  say,  that  the  silk  was  weighed 
finally  in  water,  and  with  precision,  and  I  will  here  add 
in  passing,  that  the  specific  gravity  of  this  substance  was 
found  to  be  to  that  of  water  as  1734  is  to  1000.  The 
following  phenomenon,  however,  which  I  noticed  while 
weighing  the  silk  in  water,  struck  me  forcibly. 

The  silk  being  in  the  form  of  a  skein  about  6  inches 
long,  and  tied  loosely  in  order  to  allow  the  water  readily 
to  enter  among  all  the  threads,  it  was  hung  from  one  of 
the  arms  of  an  excellent  hydrostatic  balance  in  a  large 
mass  of  distilled  water  which  had  previously  been  freed 
from  air  by  long  boiling. 

The  weight  of  the  silk  in  this  situation  having  been 
determined,  it  was  then  placed,  by  means  of  silver  pincers, 
and  without  taking  it  from  the  water,  into  a  small  glass 
vessel  of  oval  form,  about  2  inches  in  diameter  and  3 
inches  long,  and  weighed  again. 

The  weight  of  the  silk  when  weighed  in  the  small 
glass  vessel  was  sensibly  greater  than  when  it  was  weighed 
out  of  the  vessel  in  the  same  large  amount  of  water,  and 


302  On  the  Adhesion  of  the  Particles 

on  repeating  the  experiment  several  times,  the  result 
was  always  the  same. 

The  following  appeared  to  me  to  be  a  satisfactory  ex- 
planation of  this  phenomenon. 

As  silk  is  one  of  those  substances  which  can  be  wet 
by  water,  it  is  evident  that  the  particles  of  the  liquid 
which  were  in  immediate  contact  with  the  surface  of  the 
thread  must  have  remained  attached  to  it.  These  parti- 
cles, having  become  thus  fixed  and  immovable,  were  in 
contact  with  other  particles  which  still  enjoyed  their  free- 
dom of  motion,  and  these  particles  again  were  in  contact 
with  others  farther  from  the  silk,  and  so  on.  Now,  as 
the  fluidity  of  various  liquids  is  evidently  very  different, 
it  is  more  than  probable  that  no  liquid  possesses  perfect 
fluidity;  consequently  water  does  not:  and  if  any  force 
whatever  is  needed  to  separate  its  particles  and  make 
them  move  on  each  other,  it  is  evident  that,  in  this  case, 
if  a  solid  body  specifically  heavier  than  water  were 
plunged  into  a  quiet  mass  of  this  liquid,  there  should  be 
an  apparent  loss  of  weight  on  account  of  the  viscosity 
of  the  liquid,  and  this  loss  of  weight  would  be  in  pro- 
portion to  the  extent  of  the  surface  of  the  body. 

If,  for  example,  the  body  is  suspended  by  a  thread, 
the  thread  will  not  support  all  the  excess  of  the  weight 
of  the  body  over  the  weight  of  a  mass  of  the  liquid 
equal  to  the  volume  of  the  solid  body;  fora  part  of  this 
excess  would  be  supported  by  the  adhesion  which  exists 
among  those  particles  of  the  liquid  which  are  in  contact 
with  the  particles  attached  to  the  surface  of  the  body. 

This  appeared  to  me  too  evident  to  need  demonstra- 
tion or  even  further  explanation. 

In  one  of  the  experiments  in  question,  the  silk  being 
suspended  freely  in  the  water,  it  was  in  contact  with  this 


of  Liquids  to  each  other.  303 

liquid  by  a  very  great  surface  (about  550  square  inches), 
and  its  loss  of  weight  on  account  of  the  viscosity  of  the 
liquid  was  very  sensible ;  but  when  it  was  weighed  in  a 
small  vessel  which  had  been  previously  counterpoised 
very  exactly  in  the  water,  the  arm  of  the  balance  sup- 
ported all  the  excess  of  the  weight  of  the  silk  over  that 
of  an  equal  bulk  of  water  without  any  diminution. 

The  results  of  these  experiments  have  furnished  data 
for  calculating,  with  sufficient  exactness,  the  degree  of 
force  with  which  particles  of  water  adhere  to  each  other, 
when  it  is  a  question  of  causing  them  to  move  one 
upon  the  other  at  a  temperature  of  about  60°  F.,  and  I 
found  it  to  be  such  that  a  solid  body  specifically  heavier 
than  water,  having  a  surface  equal  to  368  square  inches 
(English),  when  submerged  in  water,  ought  to  lose  in 
weight,  on  account  of  the  viscosity  of  the  water,  an 
amount  equal  to  I  grain  Troy. 

The  discovery  of  this  fact  has  put  me  in  position,  not 
only  to  prove  that  all  bodies  in  nature,  the  heaviest  as 
well  as  the  lightest,  can  be  suspended  and  supported 
in  still  water,  on  account  of  its  viscosity,  provided  they 
are  reduced  to  a  sufficiently  small  size,  but  also  to  deter- 
mine by  calculation  that  a  solid  spherule  of  gold  about 
STTiF^nnr  °f  an  ^ncn  'm  diameter  would  remain  sus- 
pended in  this  manner,  as  I  have  already  announced  to 
the  Class  in  the  memoir  read  at  the  session  held  on  the 
1 6th  of  June,  the  past  year  (1806).* 

Having  announced  facts  as  remarkable  as  these,  I  re- 
frained from  entering  into  more  minute  details.  I  did 
not  even  think  it  necessary  to  observe  that,  even  if  I 
should  have  deceived  myself  somewhat  in  my  estimation 
of  the  force  of  cohesion  of  the  particles  of  water,  still,  if 

*  This  calculation  will  be  found  in  a  note  at  the  end  of  this  paper  (page  315). 


304  On  the  Adhesion  of  the  Particles 

it  be  only  granted  (and  this  cannot  be  called  into  ques- 
tion) that  the  fluidity  of  this  liquid  is  not  absolutely 
perfect,  but  that  a  certain  amount  of  force  is  necessary, 
no  matter  how  small  it  may  be,  to  separate  the  particles 
from  each  other,  this  alone  will  be  sufficient  to  establish 
all  that  I  have  asserted  with  regard  to  the  necessary  con- 
sequences of  the  adhesion  of  the  particles  of  liquids  to 
each  other. 

It  would  only  be  a  question  in  each  case  of  supposing 
that  a  solid  body  immersed  in  any  liquid  be  reduced  to 
a  sufficiently  small  size,  and  it  could  be  proved  that  it 
must  necessarily  remain  suspended  there.  But  it  is 
easy  to  see  that  the  greater  the  force  of  cohesion  be- 
tween the  particles  of  a  liquid,  the  more  capable  this 
liquid  becomes  of  holding  in  suspension  foreign  bodies 
of  all  sorts. 

Water  appeared  to  me  to  possess  this  quality  to  a  re- 
markable degree  ;  and  it  is  certain  that  if  there  had  been 
need  of  a  vehicle  for  the  nourishment  of  plants  and  ani- 
mals, one  capable  of  holding  in  suspension  and  of  trans- 
porting from  one  place  to  another  all  sorts  of  substances, 
very  different  in  weight  and  size,  without  affecting  them 
chemically,  it  would  never  have  been  possible  to  find  one 
more  fitted  for  this  purpose  than  water. 

Is  it  not  probable  that  this  is  one  of  the  principal  de- 
signs of  the  existence  of  this  liquid  in  the  economy  of 
Nature  ? 

Being  accustomed  to  see  traces  of  great  wisdom  and 
of  admirable  simplicity  in  all  those  dispositions  of 
Nature  which  I  have  been  able  to  comprehend,  I  have 
been  perhaps  too  much  inclined,  in  my  ordinary  medita- 
tions, to  admit  this  conclusion.  I  must,  however,  con- 
fess that  the  facts  which  have  seemed  to  me  to  render  it 
probable  have  made  a  deep  impression  upon  me. 


of  Liquids  to  each  other.  305 

Having  found  that  the  adhesion  of  the  particles  of 
water  to  each  other  is  so  considerable,  I  was  not  slow  to 
perceive  that  this  adhesion  ought  to  manifest  itself  in  a 
very  peculiar  and  sensible  manner  at  the  surface  of  the 
liquid  ;  and  it  was  then  that  I  saw  clearly  that  it  might 
be  possible  to  explain  in  a  satisfactory  manner  several 
phenomena  which  have  always  been  regarded  as  difficult 
of  explanation  ;  as,  for  example,  the  suspension  of  heavy 
bodies  of  small  size  which  appear  to  float  on  the  surface 
of  the  water ;  the  concave  form  taken  on  by  the  surface 
of  water  when  confined  in  a  small  vessel ;  the  change  of 
this  form  into  convex  when,  the  vessel  having  been  filled 
to  the  brim,  more  liquid  is  added;  the  suspension  of 
liquids  in  capillary  tubes,  etc. 

I  wrote,  in  the  winter  of  1800,  a  memoir  on  this  sub- 
ject, which  I  afterwards  showed  to  several  persons, 
among  others  to  Professor  Pictet,  of  Geneva,  when  he 
was  in  London  in  1801  ;  also  to  Sir  Charles  Blagden. 
The  reason  for  not  publishing  it  at  that  time  was  that  I 
needed  the  assistance  of  profound  analysis  in  order  to 
finish  it. 

When  I  arrived  at  Paris  in  the  spring  of  1802,  I  took 
advantage  of  this  occasion  to  consult  the  greatest  geom- 
eters of  the  century  on  the  embarrassing  question  which 
stood  in  my  way.  Four  persons  now  present  in  this 
Assembly  can  remember  the  circumstance.  I  desired  to 
know  the  form  which  the  vertical  middle  section  of  a 
drop  of  water,  or  other  liquid  substance,  would  take  if 
placed  on  a  plane  horizontal  surface,  supposing  that  the 
liquid  was  restrained  solely  by  the  resistance  of  a  pellicle 
exerting  a  given  force  on  its  surface. 

The  problem  appeared  very  simple,  but  its  solution 
is  extremely  difficult.  I  did  not  know  at  that  time 


306  On  the  Adhesion  of  the  Particles 

that  Segner  had  attempted  to  solve  it.  I  had  no  knowl- 
edge of  the  memoir  which  he  published  on  this  subject 
more  than  forty  years  ago  in  the  first  volume  of  the 
memoirs  of  the  Royal  Society  of  Gottingen. 

If  I  recall  these  facts,  it  is  simply  to  prove  that  I  have 
not  taken  the  liberty  of  occupying  the  attention  of  the 
Class  with  a  subject  as  difficult  as  a  research  on  the 
adhesion  of  the  particles  of  liquids,  and  the  various  phe- 
nomena dependent  upon  it,  without  previous  medita- 
tion ;  and  to  prove  that  the  opinions  which  I  have  ven- 
tured to  bring  before  it  were  adopted  a  long  time  since, 
and  have  been  often  examined  before  being  announced. 

I  have  most  certainly  nothing  more  at  heart  than  to 
preserve  the  esteem  and  deserve  the  confidence  of  every 
member  of  this  illustrious  Assembly.  The  favour  which 
they  have  shown  me  in  giving  me  the  right  to  sit  among 
them,  which  I  regard  in  the  light  of  a  very  distinguished 
honour,  as  well  as  my  respect  for  their  talents,  makes 
me  hold  it  as  a  sacred  duty  never  to  abuse  their  atten- 
tion with  trifles,  or  crude  ideas,  or  opinions  formed  in 
haste  and  ill-digested. 

If  I  ventured  to  speak  of  the  pellicle  of  the  water,  it  is 
because  I  really  believed  in  its  existence  ;  and  I  believe 
in  it  still,  and  more  firmly  than  ever. 

Allow  me  to  recall  to  the  Class  the  phenomena  which 
have  seemed  to  me  to  indicate  its  existence. 

When  I  have  seen  little  steel  needles  float  on  the  sur- 
face of  this  liquid  without  sinking  into  it,  and  even 
without  being  wet ;  when  I  have  seen  little  globules  of 
mercury  roll  about  on  the  surface  of  the  water,  then,  com- 
ing to  rest,  and  sinking  to  a  certain  depth  in  the  liquid 
without,  however,  being  -wet  by  it,  remain  as  though 
suspended  in  a  small  pocket ;  when  I  have  seen  diminu- 


of  Liquids  to  each  other.  307 

tive  spider-like  insects,  with  long  legs,  run  about  over 
the  water  without  their  feet  sinking  into  the  liquid,  or 
even  being  wet  by  it ;  .when  I  have  seen  several  minute 
bodies  at  a  distance  from  each  other,  resting  upon  the 
surface  of  the  water  contained  in  a  small  vessel,  tremble 
every  time  that  the  surface  of  the  water  was  touched 
with  the  point  of  a  needle,  —  I  have  been  unable  to 
doubt  the  existence  of  a  resisting  surface,  a  sort  of  pel- 
licle on  the  surface  of  the  liquid. 

There  is  another  phenomenon  which  seems  to  me  to 
furnish  a  demonstrative  proof  of  the  existence  of  this  re- 
sisting surface.  When  water  is  heated  in  any  vessel, 
as  soon  as  the  liquid  begins  to  become  warm  a  consider- 
able quantity  of  air  is  disengaged  in  the  form  of  spheri- 
cal bubbles,  larger  or  smaller,  which,  passing  through  the 
liquid  from  below  upwards,  escape  into  the  air.  Now 
it  very  often  happens  that  these  little  bubbles,  after 
having  traversed  the  liquid  with  great  rapidity,  are 
stopped  all  of  a  sudden  when  they  have  nearly  reached 
the  surface. 

What  is  it  that  stops  these  bubbles  if  not  a  resisting 
pellicle  at  the  surface  of  the  liquid  ? 

I  endeavoured,  but  in  vain,  to  explain  these  facts,  by 
calling  to  my  aid  the  atmospheric  air.  I  saw  clearly, 
as  I  observed  the  little  globule  of  mercury  situated  in 
its  little  pocket,  which  sank  sensibly  lower  than  the 
level  surface  of  the  water,  and  which  was  scarcely  large 
enough  to  hold  the  globule,  —  I  saw,  I  say,  that  the  film 
of  air,  which  we  might  suppose  still  attached  to  the  sur- 
face of  the  globule  (if  such  a  film  really  existed),  could 
not  be  thick  enough  to  buoy  up  this  heavy  body  and 
make  it  float,  hydrostatically,  on  the  surface  of  the  water. 
But  when  to  the  testimony  of  these  experiments  and  to 


308  On  the  Adhesion  of  the  Particles 

that  of  several  others  of  the  same  sort,  which  can  readily 
be  performed,  is  added  the  evidence  furnished  by  the 
certain  knowledge  which  we  have  of  a  strong  adhesion 
which  exists  among  the  particles  of  water,  and  of  the 
effect  which  this  adhesion  must  necessarily  produce  at 
the  surface  of  the  liquid,  it  seems  to  me  impossible  to 
call  into  doubt  the  existence  of  a  resisting  layer  extremely 
thin  at  the  surface  of  the  water. 

In  announcing  the.  existence  of  a  sort  of  pellicle  at 
the  surface  of  liquids,  I  was  far  from  thinking  that  it 
was  a  new  idea.  I  am  aware  that  several  philosophers, 
and  among  others  one  of  our  celebrated  colleagues,  M. 
Monge,  had  suspected  it  before  I  did,  but  I  think  that  I 
was  the  first  to  devise  and  perform  decisive  experiments 
which  have  established  the  fact  beyond  doubt ;  and  it  is 
certain  that  the  observations  that  I  have  published  on 
the  effect  which  the  adhesion  of  the  particles  of  liquids 
to  each  other  must  have  in  the  economy  of  Nature,  have 
been  borrowed  from  no  one. 

If  the  existence  of  a  resisting  film  at  the  surfaces  of 
liquids  has  just  been  confirmed  by  the  results  of  the 
learned  analytical  researches  of  one  of  our  celebrated  col- 
leagues, I  ought,  without  doubt,  to  regard  this  event 
as  a  proof  very  flattering  to  me,  that  my  conjectures  on 
this  subject  were  not  ill  founded. 

I  know  that  there  are  some  persons  who  imagine 
that  the  results  of  the  calculations  of  the  illustrious 
author  of  the  Mecanique  Celeste  on  the  rising  of  liquids 
in  capillary  tubes  are  opposed  to  the  opinions  which 
I  have  published  on  the  adhesion  of  the  particles  of 
liquids  to  each  other ;  but,  as  far  as  I  have  been  able  to 
understand  the  data  on  which  these  calculations  are 
founded,  it  seems  evident  to  me  that  the  attraction  with 


of  Liquids  to  each  other.  309 

which  M.  La  Place  supposes  the  particles  of  the  liq- 
uid to  be  endowed,  does  not  differ  essentially  from 
the  force  which  I  have  designated  by  the  name  adhesion ; 
and  with  regard  to  the  pellicle,  of  which  I  have  often 
spoken,  since  the  calculation  of  this  learned  geometrician 
and  philosopher  is  founded  on  the  supposition  that  the 
mutual  attractions  of  the  particles  of  the  liquid  situated 
a  certain  distance  below  the  surface  of  the  liquid  do  not 
contribute  in  any  way  to  the  rising  of  the  liquid  in  a 
capillary  tube,  nor  to  any  other  similar  effects  which  he 
has  considered,  it  seems  to  me  that  the  calculations  of 
M.  La  Place  simply  relate  to  the  force  of  cohesion  of 
the  layer  of  particles  at  the  surface,  or,  in  other  words, 
to  the  pellicle  in  question. 

I  must,  however,  confess  that  I  am  not  sufficiently 
well  versed  in  the  higher  geometry  to  understand  fully 
the  calculations  of  M.  La  Place  on  this  subject ;  and 
I  shall  take  good  care  not  to  pass  judgment  on  them. 
One  must  have,  without  doubt,  a  very  profound  acquaint- 
ance with  analytical  methods  to  feel  the  force  of  his 
demonstrations  ;  but  I  have  such  a  high  opinion  of  the 
talents  of  this  man,  learned  and  worthy  of  esteem  both 
as  a  geometrician  and  as  a  natural-philosopher,  that  I 
am  always  inclined  to  receive  his  opinions  in  matters  of 
science  (as  well  as  on  every  other  subject)  with  the 
greatest  deference. 

The  researches  to  which  I  have  sought  to  call  the 
attention  of  philosophers  would  be,  no  doubt,  of  less 
importance  if  it  was  merely  a  question  of  the  explana- 
tion of  a  few  facts,  isolated  and  of  little  utility  in  their 
applications  ;  but  the  adhesion  of  the  particles  of  liquids 
to  each  other  is  probably  the  cause  of  a  great  variety  of 
phenomena  which  affect  us  intimately  ;  and  for  this  rea- 


310  On  the  Adhesion  of  the  Particles 

son  the  subject  must  be  regarded  as  very  interesting. 
It  seems  to  me  that  it  is  to  this  adhesion,  and  to  the 
changes  of  its  intensity,  arising  from  different  circum- 
stances, that  we  must  look  for  the  proximate  cause  of 
the  growth  of  plants  and  of  animals. 

I  have  already  observed  that  the  strong  force  of  adhe- 
sion existing  among  the  particles  of  water  renders  this 
liquid  peculiarly  fitted  to  serve  as  the  vehicle  for  con- 
veying nourishment  to  all  living  beings;  and  I  think 
that  I  can  show  that  this  force  of  adhesion  can  be  very 
much  decreased,  that  this  actually  happens  very  often, 
and  that  one  of  the  necessary  consequences  of  such  a 
diminution  would  be  the  deposition  or  precipitation  of 
foreign  matters  which  this  liquid  holds  in  suspension 
on  account  of  its  viscosity. 

If  water  ascends  as  sap  in  the  capillary  tubes  of  trees 
as  far  as  the  leaves,  it  is  possible  that  it  there  undergoes 
some  change,  or  that  it  there  receives  some  addition, 
which  diminishes  its  viscosity,  and  disposes  it  in  this  way 
to  deposit  matters  which  it  holds  in  suspension  and 
which  contribute  to  the  growth  of  the  plant. 

If,  during  the  digestion  of  food  which  takes  place  in  the 
stomach,  water,  aided  perhaps  by  the  gastric  juice,  seizes 
at  first  upon  nutritive  particles  of  every  sort  which  are 
there  found  and  holds  them  in  suspension,  is  it  not 
possible  that  this  liquid  thus  loaded,  being  mixed  subse- 
quently with  a  portion  of  bile,  at  its  entrance  into  the 
intestinal  canal,  is  by  this  means  rendered  less  viscous 
and  consequently  better  fitted  to  pass  easily  through  the 
lacteal  veins,  and  more  disposed  to  yield  up  the  nutri- 
tive particles  as  it  enters  into  circulation  ? 

In  case  this  conjecture  be  well  founded,  we  ought, 
undoubtedly,  to  find  that  a  mixture  of  bile  with  water 


of  Liquids  to  each  other.  31 1 

would  diminish,  to  a  sensible  extent,  the  viscosity  of 
this  latter  liquid  ;  and  I  actually  found  by  experiments 
which  I  shall  have  the  honour  of  laying  before  the  Class 
at  some  future  time  in  detail,  that  mixing  i  part  of  bile 
with  1000  parts  of  water  diminishes  the  adhesion  of 
the  particles  of  water  to  each  other  nearly  one  third, 
that  is  to  say,  in  the  ratio  of  23  to  16  ;  and  that  if  i  part 
only  of  bile  be  mixed  with  30,000  parts  of  water,  the 
diminution  is  still  very  apparent.  In  a  mixture  of  i 
part  of  bile  with  300  parts  of  water,  the  adhesion  in 
question  is  reduced  almost  one  half. 

Milk  is  a  liquid  which  seems  to  be  already  elaborated 
and  fitted  to  serve  as  nourishment  for  animals ;  now  I 
have  found,  by  decisive  experiments,  that  the  adhesion 
among  the  particles  of  this  animal  fluid  is  less  than  that 
among  the  particles  of  water  in  the  proportion  of  13 
to  19!. 

The  adhesion  of  the  particles  of  urine  to  each  other 
varies  considerably.  I  have  found  it  from  13  i  to  16, 
that  of  water  being  19!. 

Many  persons  have  endeavoured  to  discover  the  nature 
of  diseases  by  the  examination  of  the  urine;  no  one, 
however,  as  far  as  I  know,  has  ever  proposed  to  measure 
the  force  of  adhesion  of  its  particles  to  each  other,  a 
thing  as  easy  to  determine  as  it  is  useful  to  ascertain. 

How  interesting  it  would  be  to  know  the  force  of 
adhesion  of  the  particles  of  the  gastric  juice,  of  the  pan- 
creatic juice,  of  the  lymph,  and  of  the  blood,  both  in 
health  and  in  the  various  diseases  !  Of  how  great  im- 
portance would  a  knowledge  of  these  facts  be  to  the 
physiologist  and  to  the  physician  ! 

How  useful  it  would  be  for  those  who  study  vegeta- 
ble physiology  to  know  the  adhesive  force  of  the  parti- 


312  On  the  Adhesion  of  the  Particles 

cles  of  the  sap  when  rising  and  when  descending,  and 
that  too  in  the  various  seasons  ! 

How  much  light  would  be  thrown  on  all  chemical 
operations  taking  place  in  the  wet  way,  if  we  could  esti- 
mate exactly  the  force  of  adhesion  existing  among  the 
particles  of  the  various  liquid  agents  which  there  come 
into  play  ! 

How  many  wonderful  reactions  there  are  which  seem 
to  depend  on  such  a  simple  thing  as  the  imperfect  flu- 
idity of  liquids  ! 

It  seems  to  me  that  the  facts  which  I  have  just  an- 
nounced are  of  such  a  character  as  to  excite  all  our  curi- 
osity, and  I  hasten  to  make  them  public  in  order  to 
induce  all  those  who  cultivate  the  sciences  to  assist  me 
in  these  interesting  researches. 

I  feel  deeply  that  all  that  a  single  individual  can  effect 
by  his  own  labours  during  the  course  of  his  short  life, 
in  extending  the  vast  domain  of  science,  is  unfortunately 
a  very  small  matter.  It  is  only  by  the  simultaneous 
efforts  of  a  large  number  of  men  with  good  heads  and 
skilled  hands  that  we  can  hope  to  see  a  sensible  advance 
of  this  great  enterprise,  of  which  men  will  never  see  the 
completion  ;  and  for  this  reason  those  who  with  true 
love  for  science  take  more  delight  in  seeing  its  progress 
than  in  obtaining  the  pleasures  of  gratified  vanity,  ought 
rather  to  seek  to  associate  with  themselves  a  great  num- 
ber of  zealous  and  skilful  co-labourers  than  to  endeav- 
our to  do  everything  themselves. 

Happily  for  the  progress  of  this  new  branch  of  re- 
search, the  apparatus  to  be  employed  is  portable,  and  of 
great  simplicity,  and  the  experiments  are  as  easy  to  per- 
form as  their  results  are  decisive  and  satisfactory.  In 
general,  the  only  thing  needed  will  be  an  inverted  si- 


of  Liquids  to  each  other.  313 

phon,  with  one  of  its  capillary  arms  provided  with  a 
scale  for  measuring  the  height  of  the  liquid  in  this  arm 
above  the  level  of  the  top  of  the  column  in  the  large 
arm  ;  for  it  is  now  well  established,  by  the  results  of 
conclusive  experiments,  that  the  heights  to  which  vari- 
ous liquids  rise  in  the  same  capillary  tube  are  in  pro- 
portion to  the  degrees  of  force  with  which  the  particles 
of  the  several  liquids  adhere  to  each  other. 

The  experiments  for  determining  the  diminution  pro- 
duced in  this  force  by  a  given  increase  of  temperature 
demand  more  complicated  apparatus  and  special  care. 
The  apparatus  which  I  have  used  in  this  research  is 
before  the  Class.  Since,  in  the  present  state  of  the  physi- 
cal sciences,  we  can  hardly  flatter  ourselves  that  we  are  able 
to  take  a  single  step  in  advance,  except  with  the  aid  of 
instruments  devised  with  care  and  executed  with  the 
utmost  precision,  I  always  regard  it  as  a  duty  to  afford 
the  Class  an  opportunity  of  judging,  by  its  own  obser- 
vation, of  the  excellence  of  those  used  by  me  in  such 
new  experiments  as  I  have  the  honour  of  describing  to 
the  Class. 

I  will  show,  presently,  the  way  in  which  this  appara- 
tus is  used,  and  I  will  give  to  the  Class,  at  a  subsequent 
sitting,  the  account  of  the  results  of  the  experiments  in 
which  it  has  been  employed. 

I  will  conclude  this  memoir  with  some  observations 
on  a  very  important  point,  which  should,  perhaps,  be 
still  further  elucidated. 

I  have  shown  how  I  have  proceeded  in  measuring 
that  sort  of  adhesion  of  the  particles  of  water  to  each 
other  which  produces  the  viscosity  of  this  liquid,  that 
is,  the  force  which  must  be  exerted  in  order  to  cause 
those  particles  to  move  on  each  other  ;  but  we  must 


314  On  the  Adhesion  of  the  Particles 

by  no  means  suppose  that  the  same  force  will  suffice  to 
separate  these  same  particles  from  each  other,  when  two 
of  them,  which  are  in  contact,  are  drawn  in  opposite 
directions  along  the  line  passing  through  their  centres. 

The  very  considerable  weight  of  a  drop  of  water 
which  remains  suspended  from  a  solid  body  shows 
evidently  that  this  latter  force  is  incomparably  greater 
than  I  have  found  the  former  to  be.  Now,  when  a  solid 
body  rests  on  the  surface  of  a  liquid,  it  cannot  pene- 
trate into  it  without  breaking  the  layer  of  particles 
which  are  at  this  surface,  and  which  may  be  considered 
as  forming  a  sort  of  pellicle  ;  in  order  to  break  this 
pellicle,  it  is  evidently  necessary  to  separate  the  parti- 
cles which  compose  it,  by  compelling  them  to  withdraw 
from  each  other  directly  or  nearly  in  lines  passing 
through  their  centres,  and  it  is  for  this  reason  that  small 
solid  bodies  specifically  heavier  than  water  remain  on 
the  surface  of  this  liquid  without  penetrating  into  it. 

Likewise,  when  water  issuing  from  the  upper  extrem- 
ity of  the  shortened  capillary  tube  of  an  inverted  siphon 
forms  a  small  hemispherical  mass,  resting  on  the  end  of 
the  tube  and  attached  to  its  walls,  the  convex  surface  of 
this  small  mass  of  liquid  is  formed  by  a  layer  of  parti- 
cles which  resist,  with  all  the  force  of  their  attraction 
for  each  other,  every  effort  tending  to  separate  them  ; 
and  it  is  the  resistance  of  this  single  layer  of  particles, 
or  of  several  layers  resting  immediately  one  upon  an- 
other, and  together  forming  a  sort  of  very  thin  pellicle, 
which  sustains  the  entire  weight  of  the  column  of  water 
in  the  other  arm  of  the  siphon,  which  is  situated  above 
the  level  of  the  surface  of  this  small  mass  of  liquid. 

I  have  recently  established  this  fact  by  means  of  an 
experiment,  which  I  regard  as  decisive. 


of  Liquids  to  each  other.  315 

Having  found  a  way  of  placing  in  the  middle  of  this 
small  hemispherical  mass  of  water  little  isolated  solid 
bodies  which  displaced  a  great  part  of  the  liquid  with- 
out being  wet  by  that  which  remained,  this  arrange- 
ment produced  no  change,  either  in  the  exterior  form 
or  in  the  dimensions  of  the  little  hemisphere,  or  in  the 
force  displayed  in  resisting  the  pressure  of  the  more 
elevated  column  of  water  in  the  other  arm  of  the 
siphon. 

NOTE. 

(See  page  303.)  The  following  calculation,  which  is  neither  long 
nor  difficult  to  follow,  may  be  of  service  in  understanding  what  has 
just  been  advanced. 

A  cubic  inch  of  water,  English  measure,  weighs  253.175  grains 
Troy  ;  consequently  a  spherical  mass  of  this  liquid  10.8233  mcnes  in 
diameter,  and  which  would  have  a  surface  of  368  square  inches,  would 
weigh  168,060  grains.  And  since  the  specific  gravity  of  gold  is  to 
that  of  water  as  192,581  is  to  10,000,  a  sphere  of  gold  of  the  same 
diameter  would  weigh  3,236,525  grains  in  vacuo. 

Now,  a  similar  sphere  weighed  in  water  would  lose  of  its  weight 
in  vacuo  an  amount  equal  to  the  weight  of  a  mass  of  water  of  a  volume 
equal  to  that  of  the  sphere.  It  would  weigh,  therefore,  3,236,525 

168,060=:  3,068,465  grains,  a  deduction  being  made  for  the  slight 

amount  of  its  weight  which  it  would  lose  on  account  of  the  viscos- 
ity of  the  liquid. 

Since  the  surface  of  the  globe  is  equal  to  368  square  inches,  we  see, 
from  the  result  of  the  experiment  of  which  we  have  just  given  an 
account,  that  this  decrease  of  weight  must  be  exactly  one  grain. 
Consequently  the  sphere  suspended  in  water  will  weigh  on  the  beam 
of  the  balance  only  3,068,464  grains,  and  it  will  lose  -;J—  of  its 
weight  on  account  of  the  viscosity  of  the  liquid. 

Let  us  suppose,  now,  that  the  diameter  of  this  sphere  were  10  times 
as  small,  or  1.08233  inches,  and  let  us  see  according  to  what  law  the 
effect  produced  on  the  viscosity  of  the  liquid  will  be  increased  by  this 
diminution  of  volume. 

The  volumes  and  consequently  the  weights  of  spheres  of  different 
diameters  being  as  the  cubes  of  those  diameters,  while  their  surfaces 


3 1 6  On  the  Adhesion  of  the  Particles 

are  as  the  squares  of  the  same  lines,  it  is  evident  that  the  weight  of  the 
small  sphere  mentioned  above  must  be  1000  times  less  than  the  weight 
of  the  large  sphere  (the  cube  of  10  being  1000  and  its  square  100), 
consequently  the  smaller  sphere  ought  to  weigh  in  water  only  3068.465 
grains  (deduction  being  made  for  the  effect  of  the  viscosity  of  the 
liquid),  and  its  surface  would  be  3.68  square  inches. 

Since  the  diminution  of  weight  which  was  due  to  the  viscosity  of 
the  liquid  was  only  I  grain  when  the  surface  of  the  sphere  was  368 
square  inches,  it  is  evident  that  this  diminution  ought  to  be  loo  times 
smaller,  or  —  of  a  grain,  in  the  case  of  the  smaller  globe  which  has 
100  times  less  surface  ;  now  ^  of  a  grain  in  the  case  of  a  body  which 
weighs  only  3068.465  grains  is  — ^-.  of  the  real  weight  of  the  body 
in  water,  and  by  this  amount  the  weight  will  be  diminished  on  account 
of  the  viscosity  of  the  liquid.  This  quantity  is  precisely  100  times 
more  considerable,  relatively  to  the  weight  of  the  body  in  water,  than 
we  have  found  it  to  be  in  the  case  of  a  body  10  times  as  large. 

Hence  we  may  conclude  (and  this  can  also  easily  be  shown  by  a  rigor- 
ous demonstration)  that  when  a  solid  sphere  heavier  than  water  is  sub- 
merged in  this  liquid,  the  decrease  of  weight  due  to  the  viscosity  of 
the  liquid  is  inversely  proportional  to  the  diameter  of  the  sphere. 

For  example,  if,  when  the  diameter  of  the  sphere  was  10.3233 
inches,  the  decrease  of  its  weight  in  water  due  to  the  viscosity  of 
that  liquid  is  to  its  weight  in  the  same  liquid  in  the  ratio  of  i  to 
3068465  ;  — 

The   diminution  of  weight  due  to 
the  viscosity  of  the  liquid  will  be  to 
When  the  diameter  is  reduced  to  the  weight  of  the  body  in  water 


1.08233  of  an  inch 

0.108233 

0.0108233 

0.00108233 

0.000108233 

0.0000108233 

0.00000108233 


306846.5 
30684.65 
3068.465 
306.8465 
30.68465 
3.068465 
0.3068465 


And  in  this  last  case  it  is  evident  that  the  minute  body  must  of 
necessity  remain  suspended  in  the  liquid. 

I  know  very  well  that  these  long  numerical  calculations  must  seem 
superfluous  to  geometers  accustomed  to  algebraic  calculation  ;  but  many 
persons  who  are  unacquainted  with  algebra  desire  to  have  brought 
within  their  reach  satisfactory  proofs  of  the  truth  of  a  conclusion 
which  is  given  out  to  them  as  certain,  especially  when  it  is  to  serve  as 


of  Liquids  to  each  other.  317 

the  foundation  of  a  theory  which  is  applied  to  very  interesting 
phenomena. 

As  soon  as  it  is  shown  that  the  diminution  of  weight  which  a 
sphere  plunged  into  water  experiences  as  a  result  of  the  viscosity  of  this 
liquid  is  inversely  proportional  to  the  diameter  of  the  sphere,  and 
when  we  know  the  amount  of  this  diminution  in  a  particular  case,  it 
is  easy  to  determine,  by  a  very  simple  calculation,  what  will  be  the 
diminution  taking  place  in  another  case. 

For  example,  we  can  determine  what  will  be  the  diameter  of  the 
largest  sphere  of  gold  which  will  remain  suspended  in  water  on  account 
of  the  viscosity  of  this  liquid.  Proceeding  in  this  manner,  I  found 
this  diameter  equal  to  — — .  of  an  inch. 


83.505 


[This  paper  is  translated  from  the  French  as  it  appears  in  the  Biblio- 
theque  Britannique  (Science  et  Arts),  XXXIV.  (1807),  pp.  301  -313, 
and  XXXV.  pp.  3-  16.] 


OF    THE    SLOW    PROGRESS 


SPONTANEOUS  MIXTURE  OF  LIQUIDS 

DISPOSED    TO    UNITE    CHEMICALLY   WITH    EACH 
OTHER. 

IN  order  to  obtain  the  most  exact  knowledge  of  the 
nature  of  the  forces  which  act  in  the  chemical  com- 
bination of  various  bodies,  one  must  study  the  phe- 
nomena of  these  operations,  not  only  in  their  results, 
but  more  especially  in  their  progress. 

When  we  mix  together  two  liquids  which  we  wish 
to  have  unite,  we  take  care  to  shake  them  violently,  in 
order  to  facilitate  their  union  ;  it  might,  however,  be 
very  interesting  to  know  what  would  happen,  if,  instead 
of  mixing  them,  they  were  simply  brought  into  contact 
by  placing  one  upon  the  other  in  the  same  vessel,  tak- 
ing care  to  cause  the  lighter  to  rest  upon  the  heavier. 

Will  the  mixture  take  place  under  such  circumstan- 
ces ?  and  with  what  degree  of  rapidity  ?  These  are 
questions  interesting  alike  to  the  chemist  and  to  the 
natural-philosopher. 

The  result  would  depend,  without  doubt,  on  several 
circumstances  which  we  might  be  able  to  anticipate,  and 
the  effects  of  which  we  might  perhaps  estimate  a  priori. 
But  since  the  results  of  experiments,  when  they  are 
well  made,  are  incomparably  more  satisfactory  than  con- 
clusions drawn  from  any  course  of  reasoning,  especially 
in  the  case  of  the  mysterious  operations  of  Nature,  I 


Of  the  Progress  of  the  Mixture  of  Liquids,  etc.     3 1 9 

propose  to  speak  before  this  illustrious  Assembly  sim- 
ply of  experiments  that  I  have  performed. 

Having  procured  a  cylindrical  vessel  of  clear  white 
glass  i  inch  8  lines  in  diameter,  and  8  inches  high, 
provided  with  a  scale  divided  from  the  bottom  upwards 
into  inches  and  lines,  I  put  it  on  a  firm  table  in  the 
middle  of  a  cellar,  where  the  temperature,  which 
seemed  to  be  tolerably  constant,  was  64  degrees  of  Fah- 
renheit's scale. 

I  then  poured  into  this  vessel,  with  due  precautions, 
a  layer  of  a  saturated  aqueous  solution  of  muriate 
of  soda,  3  inches  in  thickness,  and  on  to  this  a  layer 
of  the  same  thickness  of  distilled  water.  This  opera- 
tion was  performed  in  such  a  way  that  the  two  liquids 
lay  one  upon  the  other  without  being  mixed,  and  when 
everything  was  at  rest  I  let  a  large  drop  of  the  essential 
oil  of  cloves  fall  into  the  vessel.  This  oil  being  spe- 
cifically heavier  than  water,  and  lighter  than  the  solution 
of  muriate  of  soda  on  which  the  water  rested,  the  drop 
descended  through  the  layer  of  water ;  when,  however, 
it  reached  the  neighbourhood  of  the  surface  of  the  saline 
solution  it  remained  there,  forming  a  little  spherical 
ball,  which  maintained  its  position  at  rest,  as  though  it 
were  suspended,  near  the  axis  of  the  vessel. 

I  then  poured,  with  proper  precautions,  a  layer  of 
olive  oil  four  lines  in  thickness  on  to  the  surface  of  the 
water,  to  prevent  the  contact -of  the  air  with  the  liquid, 
and  having  observed,  by  means  of  the  scale  attached  to 
the  vessel,  and  noted  down  in  a  register,  the  height  at 
which  the  little  ball  was  suspended,  I  withdrew,  and, 
locking  the  door,  I  left  the  apparatus  to  itself  for 
twenty-four  hours. 

In  a  preliminary  experiment,  made  to  determine  in 


320     Of  the  Progress  of  the  spontaneous  Mixture 

what  proportions  the  saturated  solution  should  be  mixed 
with  distilled  water,  that  the  mixture  might  have  the 
same  specific  gravity  as  the  oil  of  cloves,  I  found  that 
a  mixture  composed  of  i  measure  of  the  solution  and 
9  measures  of  distilled  water  had  a  slightly  higher  spe- 
cific gravity  than  the  oil ;  but  with  10  measures  of  dis- 
tilled water  the  oil  sank  in  the  mixture. 

As  the  little  ball  of  oil,  designed  to  serve  me  as  an 
index,  was  suspended  a  very  little  above  the  upper  sur- 
face of  the  layer  of  the  saturated  solution,  this  showed 
me  that  the  precautions  which  I  had  taken  were  suffi- 
cient to  prevent  the  mixing  of  the  distilled  water  and 
the  saline  solution  when  I  put  one  upon  the  other,  and 
I  knew  that  this  mixture  could  not  take  place  subse- 
quently without  causing  at  the  same  time  my  little 
sentinel,  which  was  there  to  warn  me  of  this  event,  to 
ascend. 

There  was,  however,  a  single  source  of  error  which 
I  was  obliged  to  guard  against.  I  had  observed,  in 
other  experiments  of  this  kind,  that  the  air  which  was 
disseminated  through  or  dissolved  in  water  containing 
in  solution  a  small  quantity  of  muriate  of  soda  left 
the  liquid,  and  attached  itself  to  the  little  ball  of  oil  of 
cloves  which  I  had  introduced  into  it,  and,  having 
formed  on  top  of  it  a  little  bubble  scarcely  visible, 
caused  it  to  ascend  in  the  liquid,  even  when  the  density 
of  the  liquid  had  not  changed  at  all. 

To  prevent  this  accident,  I  boiled  for  some  time 
both  the  saturated  solution  and  the  distilled  water  em- 
ployed in  the  experiment,  in  order  to  free  them  from 
air,  and,  for  the  same  reason,  I  subsequently  covered 
the  water  with  a  layer  of  olive  oil  to  prevent  the  contact 
of  this  water  with  the  atmospheric  air. 


of  Liquids  disposed  to  unite  with  exch  other.     32  i 

After  the  little  apparatus  mentioned  above  had  been 
left  to  itself  for  twenty-four  hours,  I  entered  the  cellar, 
taking  a  light  in  order  to  note  the  progress  of  the  ex- 
periment, and  I  found  that  the  little  ball  had  risen  3  lines. 

The  next  day,  at  the  same  hour,  I  observed  the 
ball  again,  and  I  found  that  it  had  risen  about  3  lines 
more  ;  and  thus  it  continued  to  ascend  about  3  lines  a 
day  for  six  days,  when  I  put  an  end  to  the  experiment. 

I  afterwards  made  nearly  similar  experiments  with 
saturated  aqueous  solutions  of  nitrate  of  potash,  car- 
bonate of  potash,  and  carbonate  of  soda.  In  each  of 
these  experiments  the  surface  of  the  saturated  solution 
was  covered  with  a  layer  of  distilled  water  3  inches  in 
thickness,  but  the  surface  of  this  layer  of  water  was 
not  covered  by  a  layer  of  olive  oil ;  it  was  exposed  to 
the  air,  and  this  circumstance  was,  without  doubt,  the 
reason  that  the  daily  results  of  a  single  experiment  were 
not  always  the  same  two  days  in  succession. 

The  little  ball  of  oil  of  cloves,  which  served  as  an 
index  to  mark  the  progress  of  the  mixture  of  the  satu- 
rated solution  with  the  distilled  water  resting  upon  it, 
ascended  usually  2  or  3  lines  in  twenty-four  hours,  but 
sometimes  I  found  that  it  had  left  its  position  and  had 
risen  to  the  very  surface  of  the  water. 

In  such  cases  it  was,  without  doubt,  borne  upwards 
by  the  air  which  it  had  attracted  from  the  liquid  ;  for 
when  I  allowed  a  fresh  drop  of  the  same  oil  to  fall  into 
the  water,  I  found  that  it  never  failed  to  descend  im- 
mediately in  the  liquid,  and  to  take  up  its  position  2  or 
3  lines  above  the  level  at  which,  the  day  before,  I  had 
found  the  ball  which  had  now  left  its  place. 

In  the  experiments  made  with  solutions  of  carbonate 
of  soda  and  carbonate  of  potash,  the  balls  of  oil 


322      Of  the  Progress  of  the  spontaneous  Mixture 

changed  in  appearance  by  the  end  of  two  or  three 
days  ;  from  being  transparent,  they  became  semi-opaque 
and  of  a  whitish  color ;  they  changed  at  the  same  time 
with  regard  to  their  specific  gravity  as  well,  and  became 
a  little  lighter.  These  changes  were  evidently  due  to 
the  beginning  of  saponification. 

This  accidental  circumstance  made  it  necessary  for 
me  to  renew  each  day  the  drop  of  oil  which  served  as 
the  index,  allowing  the  others  to  pursue  their  way  to 
the  surface  of  the  liquid  without  paying  any  further 
attention  to  them. 

By  using  as  indices  little  glass  balloons  of  proper 
size  and  thickness,  instead  of  the  drops  of  oil,  the 
inconveniences  arising  from  the  saponification  of  the 
oil  might  be  avoided. 

But  without  spending  more  time  on  the  details  of 
these  experiments,  I  hasten  to  return  to  their  results. 
They  showed  that  the  mixture  went  on  continually,  but 
very  slowly,  between  the  various  aqueous  solutions 
employed  and  the  distilled  water  resting  upon  them. 

There  is  nothing  in  this  result  to  excite  the  surprise 
of  any  one,  especially  of  chemists,  unless  it  is  the  ex- 
treme slowness  of  the  progress  of  the  mixture  in  ques- 
tion. The  fact,  however,  gives  occasion  for  an  inquiry 
of  the  greatest  importance,  which  is  far  from  being  easy 
to  solve. 

Does  this  mixture  depend  upon  a  peculiar  force  of 
attraction  different  from  the  attraction  of  universal 
gravitation,  a  force  which  has  been  designated  by  the 
name  of  chemical  affinity  ?  Or  is  it  simply  a  result  of 
motions  in  the  liquids  in  contact,  caused  by  changes 
in  their  temperatures  ?  Or  is  it,  perhaps,  the  result  of 
a  peculiar  and  continual  motion  common  to  all  liquids, 


of  Liquids  disposed  to  unite  with  each  other.     323 

caused  by  the  instability  of  the  equilibrium  existing 
among  their  molecules  ? 

I  am  very  far  from  assuming  to  be  able  to  solve  this 
great  problem,  but  it  has  often  been  the  subject  of  my 
thoughts,  and  I  have  made  at  different  times  a  consid- 
erable number  of  experiments  with  a  view  of  throwing 
light  into  the  profound  darkness  with  which  the  subject 
is  shrouded  on  every  side. 

At  a  subsequent  sitting  of  the  Class,  I  shall  have  the 
honour  of  giving  an  account  of  the  continuation  of  my 
researches  on  this  interesting  subject. 

[This  paper  is  translated  from  the  Memoires  de  1'Institut,  etc.,  VIII., 
ii.,  pp.  100-115.] 


OF   THE   USE   OF   STEAM 


VEHICLE    FOR    TRANSPORTING    HEAT. 

MANY  attempts  have  been  made,  at  different 
periods,  to  heat  liquids  by  means  of  steam  in- 
troduced into  them  ;  but  most  of  these  have  failed ; 
and,  indeed,  until  it  was  known  that  fluids  are  non-con- 
ductors of  heat,  and,  consequently,  that  heat  cannot 
be  made  to  descend  in  them  (which  is  a  recent  discov- 
ery), these  attempts  could  hardly  succeed;  for,  in 
order  to  their  being  successful,  it  is  absolutely  necessary 
that  the  tube  which  conveys  the  hot  steam  should  open 
into  the  lowest  part  of  the  vessel  which  contains  the 
liquid  to  be  heated,  or  nearly  on  a  level  with  its  bottom; 
but  as  long  as  the  erroneous  opinion  obtained,  that  heat 
could  pass  in  fluids  in  all  directions y  there  did  not  appear 
to  be  any  reason  for  placing  the  opening  of  the  steam- 
tube  at  the  bottom  of  the  vessel,  while  many  were  at  hand 
which  pointed  out  other  places  as  being  more  convenient 
for  it. 

But  to  succeed  in  heating  liquids  by  steam,  it  is  ne- 
cessary, not  only  that  the  steam  should  enter  the  liquid 
at  the  bottom  of  the  vessel  which  contains  it,  but  also 
that  it  should  enter  it  coming  from  above. 

The  steam-tube  should  be  in  a  vertical  position,  and 
the  steam  should  descend  through  it  previous  to  its 
entering  the  vessel,  and  mixing  with  the  liquid  which  it 


Of  the  Use  of  Steam.  325 

is  to  heat;  otherwise  this  liquid  will  be  in  danger  of 
being  forced  back  by  this  opening  into  the  steam-boiler  : 
for,  as  the  hot  steam  is  suddenly  condensed  on  coming 
into  contact  with  the  cold  liquid,  a  vacuum  is  necessarily 
formed  in  the  end  of  the  tube;  into  which  vacuum  the 
liquid  in  the  vessel,  pressed  by  the  whole  weight  of 
the  incumbent  atmosphere,  will  rush  with  great  force 
and  with  a  loud  noise ;  but  if  this  tube  be  placed  in  a 
vertical  position,  and  if  it  be  made  to  rise  to  the  height 
of  six  or  seven  feet  above  the  level  of  the  surface  of  the 
liquid  which  is  to  be  heated,  the  portion  of  the  liquid 
which  is  thus  forced  into  the  lower  end  of  the  tube  will 
not  have  time  to  rise  to  that  height  before  it  will  be  met 
by  steam,  and  obliged  to  return  back  into  the  vessel. 

There  will  be  no  difficulty  in  arranging  the  apparatus 
in  such  a  manner  as  effectually  to  prevent  the  liquid  to 
be  heated  from  being  forced  backwards  into  the  steam- 
boiler  ;  and  when  this  is  done,  and  some  other  neces- 
sary precautions  to  prevent  accidents  are  taken,  steam 
may  be  employed,  with  great  advantage,  for  heating 
liquids,  and  for  keeping  them  hot  in  a  variety  of  cases 
in  which  fire,  applied  immediately  to  the  bottoms  of  the 
containing  vessels,  is  now  used. 

In  dyeing,  for  instance,  in  bleaching,  and  in  brewing, 
and  in  the  processes  of  many  other  arts  and  manufac- 
tures, the  adoption  of  this  method  of  applying  heat 
would  be  attended  not  only  with  a  great  saving  of 
labour  and  of  fuel,  but  also  of  a  considerable  saving 
of  expense  in  the  purchase  and  repairs  of  boilers,  and 
of  other  expensive  machinery :  for,  when  steam  is  used 
instead  of  fire,  for  heating  their  contents,  boilers  may 
be  made  extremely  thin  and  light;  and  as  they  may 
easily  be  supported  and  strengthened  by  hoops  and 


326  Of  the  Use  of  Steam 

braces  of  iron,  and  other  cheap  materials,  they  will  cost 
but  little,  and  seldom  stand  in  need  of  repairs. 

To  these  advantages  we  may  add  others  of  still  greater 
importance.  Boilers  intended  to  be  heated  in  this  man- 
ner may,  without  the  smallest  difficulty,  be  placed  in  any 
part  of  a  room,  at  any  distance  from  the  fire,  and  in 
situations  in  which  they  may  be  approached  freely  on 
every  side.  They  may,  moreover,  easily  be  so  surrounded 
with  wood,  or  with  other  cheap  substances  which  form 
warm  covering,  as  most  completely  to  confine  the  heat 
within  them  and  prevent  its  escape.  The  tubes  by 
which  the  steam  is  brought  from  the  principal  boiler 
(which  tubes  may  conveniently  be  suspended  just  below 
the  ceiling  of  the  room)  may,  in  like  manner,  be  cov- 
ered so  as  almost  entirely  to  prevent  all  loss  of  heat  by 
the  surfaces  of  them,  and  this  to  whatever  distances 
they  may  be  made  to  extend. 

In  suspending  these  steam-tubes,  care  must,  however, 
be  taken  to  lay  them  in  a  situation  not  perfectly  horizon- 
tal^ under  the  ceiling,  but  to  incline  them  at  a  small 
angle,  making  them  rise  gradually  from  their  junction 
with  the  top  of  a  large  vertical  steam-tube,  which  con- 
nects them  with  the  steam-boiler,  quite  to  their  farthest 
extremities  ;  for,  when  these  tubes  are  so  placed,  it  is 
evident  that  all  the  water  formed  in  them,  in  conse- 
quence of  the  condensation  of  the  steam  in  its  passage 
through  them,  will  run  backwards,  and  fall  into  the 
boiler,  instead  of  accumulating  in  them  and  obstructing 
the  passage  of  the  steam  (which  it  would  not  fail  to  do 
were  there  any  considerable  bends  or  wavings,  upwards 
and  downwards,  in  these  tubes),  or  of  running  forward 
and  descending  with  the  steam  into  the  vessels  contain- 
ing the  liquids  to  be  heated,  —  which  would  happen  if 


as  a  Vehicle  for  transporting  Heat.  327 

these  tubes  inclined  downwards^  instead  of  inclining  up- 
wards, as  they  recede  from  the  boiler. 

In  order  that  clear  and  distinct  ideas  may  be  formed 
of  the  various  parts  of  this  apparatus,  even  without 
figures,  I  shall  distinguish  each  part  of  it  by  a  specific 
name.  The  vessel  in  which  water  is  boiled  in  order  to 
generate  steam  —  and  which,  in  its  construction,  may  be 
made  to  resemble  the  boiler  of  a  steam-engine  —  I  shall 
call  the  steam-boiler;  the  vertical  tube  which,  rising 
up  from  the  top  of  the  boiler,  conveys  the  steam  into 
the  tubes  (nearly  horizontal)  which  are  suspended  from 
the  ceiling  of  the  room,  I  shall  call  the  steam-reservoir. 
To  the  horizontal  tubes  I  shall  give  the  name  of  conduc- 
tors of  steam;  and  to  the  (smaller)  tubes  which,  de- 
scending perpendicularly  from  these  horizontal  conductors, 
convey  the  steam  to  the  liquids  which  are  to  be  heated, 
I  shall  exclusively  appropriate  the  appellation  of  steam- 
tubes. 

The  vessels  in  which  the  liquids  that  are  to  be  heated 
are  put,  I  shall  call  the  containing  vessels.  These  vessels 
may  be  made  of  any  form  ;  and,  in  many  cases,  they 
may,  without  any  inconvenience,  be  constructed  of  wood, 
or  of  other  cheap  materials,  instead  of  being  made  of 
costly  metals,  by  which  means  a  very  heavy  expense  may 
be  avoided ;  or  they  may  be  merely  pits  sunk  in  the 
ground,  and  lined  with  stone  or  with  bricks. 

Each  steam-tube  must  descend  perpendicularly  from  the 
horizontal  conductor  with  which  it  is  connected,  to  the 
level  of  the  bottom  of  the  containing  vessel  to  which  it 
belongs;  and,  moreover,  must  be  furnished  with  a  good 
cock,  perfectly  steam-tight,  which  may  best  be  placed 
at  the  height  of  about  six  feet  above  the  level  'of  the 
floor  of  the  room. 


328  Of  the  Use  of  Steam 

This  steam-tube  may  either  descend  within  the  vessel  to 
which  it  belongs,  or  on  the  outside  of  it,  as  shall  be  found 
most  convenient.  If  it  comes  down  on  the  outside  of 
the  vessel,  it  must  enter  it  at  its  bottom  by  a  short 
horizontal  bend ;  and  its  junction  with  the  bottom  of 
the  vessel  must  be  well  secured,  to  prevent  leakage.  If 
it  comes  down  into  the  vessel  on  the  inside  of  it,  it 
must  descend  to  the  bottom  of  it,  or  at  least  to  within 
a  very  few  inches  of  the  bottom  of  it ;  otherwise  the  li- 
quid in  the  vessel  will  not  be  uniformly  or  equally  heated. 

When  the  steam-tube  is  brought  down  on  the  inside 
of  the  containing  vessel,  it  may  either  come  down  per- 
pendicularly and  without  touching  the  sides  of  it,  or  it 
may  come  down  on  one  side  of  the  vessel  and  in  con- 
tact with  it. 

When  several  steam-tubes  belonging  to  different  con- 
taining-vessels  are  connected  with  one  and  the  same 
horizontal  steam-conductor,  the  upper  end  of  each  of 
these  tubes,  instead  of  being  simply  attached  by  solder 
or  by  rivets  to  the  under  side  of  the  conductor,  must 
enter  at  least  one  inch  within  the  cavity  of  it ;  otherwise 
the  water  resulting  from  a  condensation  of  a  part  of  the 
steam  in  the  conductor  by  the  cold  air  which  surrounds 
it,  instead  of  finding  its  way  back  into  the  steam-boiler, 
will  descend  through  the  steam-tubes,  and  mix  with  the 
liquids  in  the  vessels  below ;  but  when  the  open  ends 
of  these  tubes  project  upwards  within  the  steam-conductor  y 
though  it  be  but  to  a  small  height  above  the  level  of  its 
under  side,  it  is  evident  that  this  accident  cannot  happen. 

It  is  not  necessary  to  observe  here,  that,  in  order  that 
the  ends  of  the  steam-tubes  may  project  within  the  hori- 
zontal conductor,  the  diameters  of  the  former  must  be 
considerably  less  than  the  diameter  of  the  latter. 


as  a  Vehicle  for  transporting  Heat.  329 

To  prevent  the  loss  of  heat  arising  from  the  cooling 
of  the  different  tubes  through  which  the  steam  must 
pass  in  coming  from  the  boiler,  all  those  tubes  should 
be  well  defended  from  the  cold  air  of  the  atmosphere, 
by  means  of  warm  covering ;  but  this  may  easily  be 
done,  and  at  a  very  trifling  expense.  The  horizontal 
conductors  may  be  enclosed  within  square  wooden  tubes, 
and  surrounded  on  every  side  by  charcoal  dust,  fine 
sawdust,  or  even  by  wool ;  and  the  steam-tubes,  as 
well  as  the  reservoir  of  steam,  may  be  surrounded,  first 
by  three  or  four  coatings  of  strong  paper,  firmly  attached 
to  them  by  paste  or  glue,  and  covered  with  a  coating 
of  varnish,  and  then  by  a  covering  of  thick  coarse 
cloth.  It  will  likewise  be  advisable  to  cover  the  hori- 
zontal conductors  with  several  coatings  of  paper ;  for,  if 
the  paper  be  put  on  to  them  while  it  is  wet  with  the 
paste  or  glue,  and  if  care  be  taken  to  put  it  on  in  long 
slips  or  bands,  wound  regularly  round  the  tube  in  a 
spiral  line  from  one  end  of  it  to  the  other,  this  cover- 
ing will  be  useful,  not  only  by  confining  more  effectually 
the  heat,  but  also  by  adding  very  much  to  the  strength 
of  the  tube,  and  rendering  it  unnecessary  to  employ 
thick  and  strong  sheets  of  metal  in  the  construction 
of  it. 

However  extraordinary  and  incredible  it  may  appear, 
I  can  assert  it  as  a  fact,  which  I  have  proved  by  repeated 
experiments,  that  if  a  hollow  tube,  constructed  of  sheet 
copper  jV  of  an  inch  in  thickness,  be  covered  by  a  coat- 
ing only  twice  as  thick,  or  ^  of  an  inch  in  thickness, 
formed  of  layers  of  strong  paper,  firmly  attached  to  it 
by  good  glue,  the  strength  of  the  tube  will  be  more  than 
doubled  by  this  covering. 

I   found  by  experiments,   the   most  unexceptionable 


330  Of  the  Use  of  Steam 

and  decisive,  — of  which  I  intend  at  some  future  period 
to  give  to  the  public  a  full  and  detailed  account,  —  that 
the  strength  of  paper  is  such,  when  several  sheets  of  it 
are  firmly  attached  together  with  glue,  that  a  solid  cylin- 
der of  this  substance,  the  transverse  section  of  which 
should  amount  to  only  one  superficial  inch,  would  sus- 
tain a  weight  of  30,000  pounds  avoirdupois,  or  above 
13  tons,  suspended  to  it,  without  being  pulled  asunder 
or  broken. 

The  strength  of  hemp  is  still  much  greater,  when  it  is 
pulled  equally  in  the  direction  of  the  length  of  its  fibres. 
I  found,  from  the  results  of  my  experiments  with  this  sub- 
stance, that  a  cylinder  of  the  size  above  mentioned,  com- 
posed of  the  straight  fibres  of  hemp  glued  together,  would 
sustain  92,000  pounds  without  being  pulled  asunder. 

A  cylinder  of  equal  dimensions,  composed  of  the 
strongest  iron  I  could  ever  meet  with,  would  not  sus- 
tain more  than  66,000  pounds  weight;  and  the  iron 
must  be  very  good  not  to  be  pulled  asunder  with  a 
weight  equal  to  55,000  pounds  avoirdupois. 

I  shall  not,  in  this  place,  enlarge  on  the  many  advan- 
tages that  may  be  derived  from  a  knowledge  of  these 
curious  facts.  I  have  mentioned  them  now,  in  order 
that  they  may  be  known  to  the  public ;  and  that  ingen- 
ious men,  who  have  leisure  for  these  researches,  may  be 
induced  to  turn  their  attention  to  a  subject,  not  only 
very  interesting  on  many  accounts,  but  which  promises 
to  lead  to  most  important  improvements  in  mechanics. 

I  cannot  return  from  this  digression  without  just 
mentioning  one  or  two  results  of  my  experimental 
investigations  relative  to  the  force  of  cohesion,  or 
strength  of  bodies,  which  certainly  are  well  calculated 
to  excite  the  curiosity  of  men  of  science. 


as  a  Vehicle  for  transporting  Heat.  331 

The  strength  of  bodies  of  different  sizes,  similar  in  form 
and  composed  of  the  same  substance^ —  or  the  forces  by 
which  they  resist  being  pulled  asunder  by  weight  sus- 
pended to  them,  and  acting  in  the  direction  of  their 
lengths,  —  is  not  in  the  simple  ratio  of  the  areas  of  their 
transverse  sections,  or  of  their  fractures^  but  in  a  higher 
ratio ;  and  this  ratio  is  different  in  different  sub- 
stances. 

The  form  of  a  body  has  a  considerable  influence  on 
its  strength,  even  when  it  is  -pulled  in  the  direction  of  its 
length. 

All  bodies,  even  the  most  brittle,  appear  to  be  torn 
asunder^  or  their  particles  separated,  or  fibres  broken, 
one  after  the  other ;  and  hence  it  is  evident  that  that  form 
must  be  most  favourable  to  the  strength  of  any  given 
body,  pulled  in  the  direction  of  its  length,  which  enables 
the  greatest  number  of  its  particles,  or  longitudinal 
fibres,  to  be  separated  to  the  greatest  possible  distance 
short  of  that  at  which  the  force  of  cohesion  is  over- 
come, before  any  of  them  have  been  forced  beyond  that 
limit. 

It  is  more  than  probable  that  the  apparent  strength 
of  different  substances  depends  much  more  on  the 
number  of  their  particles  that  come  into  action  before 
any  of  them  are  forced  beyond  the  limits  of  the  attrac- 
tion of  cohesion,  than  on  any  specific  difference  in  the 
intensity  of  that  force  in  those  substances. 

But  to  return  to  the  subject  more  immediately  under 
consideration.  As  it  is  essential  that  the  steam  em- 
ployed in  heating  liquids,  in  the  manner  before  described, 
should  enter  the  containing  vessel  at  or  very  near  its 
bottom,  it  is  evident  that  this  steam  must  be  sufficiently 
strong  or  elastic  to  overcome  not  only  the  pressure 


332  Of  the  Use  of  Steam 

of  the  atmosphere,  but  also  the  additional  pressure  of 
the  superincumbent  liquid  in  the  vessel  ;  the  steam- 
boiler  must  therefore  be  made  strong  enough  to  con- 
fine the  steam,  when  its  elasticity  is  so  much  increased, 
by  means  of  additional  heat,  as  to  enable  it  to  overcome 
that  resistance.  This  increase  of  the  elastic  force  of  the 
steam  need  not,  however,  in  any  case,  exceed  a  pressure 
of  five  or  six  pounds  upon  a  square  inch  of  the  boiler, 
or  one  third part ,  or  one  half,  of  an  atmosphere. 

It  is  not  necessary  for  me  to  observe  here,  that  in 
this  and  also  in  all  other  cases  where  steam  is  used  as  a 
vehicle  for  conveying  heat  from  one  place  to  another,  it 
is  indispensably  necessary  to  provide  safety-halves  of 
two  kinds,  —  the  one  for  letting  a  part  of  the  steam 
escape,  when,  on  the  fire  being  suddenly  increased,  the 
steam  becomes  so  strong  as  to  expose  the  boiler  to  the 
danger  of  being  burst  by  it;  *  the  other  for  admitting 
air  into  the  boiler,  when,  in  consequence  of  the  diminu- 
tion of  the  heat,  the  steam  in  the  boiler  is  condensed, 
and  a  vacuum  is  formed  in  it ;  and  when,  without  this 
valve,  there  would  be  danger,  either  of  the  sides  of  the 
boiler  being  crushed,  and  forced  inwards  by  the  pressure 
of  the  atmosphere  from  without,  or  of  the  liquid  in 
the  containing  ves'sels  being  forced  upwards  into  the 
horizontal  steam-conductors,  and  from  thence  into  the 
steam-boiler.  The  last-mentioned  accident,  however, 
cannot  happen,  unless  the  cocks  in  some  of  the  steam- 
tubes  are  left  open.  The  two  valves  effectually  pre- 
vent all  accidents. 


*  The  steam  which  escapes  out  of  the  boiler  through  the  safety-valve  may  very 
easily  be  made  to  pass  into  the  reservoir  of  water  which  feeds  the  boiler,  and  be  con- 
densed there;  which  will  warm  that  water,  and  by  that  means  save  a  quantity  of  heat 
which  otherwise  would  escape  into  the  atmosphere  and  be  lost. 


as  a  Vehicle  for  transporting  Heat.  333 

The  reader  will,  no  doubt,  be  more  disposed  to  pay 
attention  to  what  has  here  been  advanced  on  this  inter- 
esting subject,  when  he  is  informed  that  the  proposed 
scheme  has  already  been  executed  on  a  very  large  scale, 
and  with  complete  success  ;  and  that  the  above  details 
are  little  more  than  exact  descriptions  of  what  actually 
exists. 

A  great  mercantile  and  manufacturing  house  at  Leeds, 
that  of  Messrs.  Gott  and  Company,  had  the  courage,  not- 
withstanding the  mortifying  prediction  of  all  their 
neighbours,  and  the  ridicule  with  which  the  scheme  was 
attempted  to  be  treated,  to  erect  a  dyeing-house^  on  a  very 
large  scale  indeed,  on  the  principles  here  described  and 
recommended. 

On  my  visit  to  Leeds  in  the  summer  of  the  year 
1800,  I  waited  on  Mr.  Gott,  who  was  then  mayor  of 
the  town,  and  who  received  me  with  great  politeness, 
and  showed  me  the  cloth-halls  and  other  curiosities  of 
the  place ;  but  nothing  he  showed  me  interested  me 
half  so  much  as  his  own  truly  noble  manufactory  of 
superfine  woollen  cloths. 

I  had  seen  few  manufactories  so  extensive,  and  none 
so  complete  in  all  its  parts.  It  was  burnt  to  the  ground 
the  year  before,  and  had  just  been  rebuilt  on  a  larger 
scale,  and  with  great  improvements  in  almost  every 
one  of  its  details. 

The  reader  may  easily  conceive  that  I  felt  no  small 
degree  of  satisfaction,  on  going  into  the  dyeing-house, 
to  find  it  fitted  up  on  principles  which  I  had  some  share 
in  bringing  into  repute,  and  which  Mr.  Gott  told  me 
he  had  adopted  in  consequence  of  the  information  he 
had  acquired  in  the  perusal  of  my  Seventh  Essay. 

He  assured   me  that  the  experiment  had  answered, 


334  Of  the  Use  of  Steam 

even  far  beyond  his  most  sanguine  expectations  ;  and, 
as  a  strong  proof  of  the  utility  of  the  plan,  he  informed 
me  that  his  next-door  neighbour,  who  is  a  dyer  by  pro- 
fession, and  who  at  first  was  strongly  prejudiced  against 
these  innovations,  had  adopted  them,  and  is  now  con- 
vinced that  they  are  real  improvements. 

Mr.  Gott  assured  me  that  he  had  no  doubt  but  they 
would  be  adopted  by  every  dyer  in  Great  Britain  in  the 
course  of  a  very  few  years. 

The  dyeing-house  of  Messrs.  Gott  and  Company, 
which  is  situated  on  the  ground  floor  of  the  principal 
building  of  the  manufactory,  is  very  spacious,  and  con- 
tains a  great  number  of  coppers,  of  different  sizes  ;  and  as 
these  vessels,  some  of  which  are  very  large,  are  distributed 
about  promiscuously,  and  apparently  without  any  order 
in  their  arrangement,  in  two  spacious  rooms,  —  each 
copper  appearing  to  be  insulated,  and  to  have  no  con- 
nection whatever  with  the  others,  —  all  of  them  to- 
gether form  a  very  singular  appearance. 

The  rooms  are  paved  with  flat  stones,  and  the  brims 
of  all  the  coppers,  great  and  small,  are  placed  at 
the  same  height  (about  three  feet)  above  the  pavement. 
Some  of  these  coppers  contain  upwards  of  1800  gallons  ; 
and  they  are  all  heated  by  steam  from  one  steam-boiler^ 
which  is  situated  in  a  corner  of  one  of  the  rooms, 
almost  out  of  sight. 

The  horizontal  tubes,  which  serve  to  conduct  the 
steam  from  the  boiler  to  the  coppers,  are  suspended 
just  below  the  ceiling  of  the  rooms :  they  are  made, 
some  of  lead  and  some  of  cast-iron,  and  are  from 
four  to  five  inches  in  diameter  ;  but  when  I  saw  them, 
they  were  naked,  or  without  any  covering  to  confine 
the  heat.  On  my  observing  to  Mr.  Gott  that  coverings 


as  a  Vehicle  for  transporting  Heat.  335 

for  them  would  be  useful,  he  told  me  that  it  was 
intended  that  they  should  be  covered,  and  that  coverings 
would  be  provided  for  them. 

The  vertical  steam-tubes^  by  which  the  steam  passes 
down  from  the  horizontal  steam-conductors  into  the  cop- 
pers, are  all  constructed  of  lead  ;  and  are  from  -|  of  an 
inch  to  2j  inches  in  diameter,  being  made  larger  or 
smaller  according  to  the  sizes  of  the  coppers  to  which 
they  belong.  These  steam-tubes  all  pass  down  on  the 
outsides  of  their  coppers,  and  enter  them  horizontally  at 
the  level  of  their  bottoms.  Each  copper  is  furnished 
with  a  brass  cock,  for  letting  off  its  contents;  and  it  is 
rilled  with  water  from  a  cistern  at  a  distance,  which  is 
brought  to  it  by  a  leaden  pipe.  The  coppers  are  all 
surrounded  by  thin  circular  brick  walls,  which  serve  not 
only  to  support  the  coppers,  but  also  to  confine  the 
heat. 

The  rapidity  with  which  these  coppers  are  heated  by 
means  of  steam  is  truly  astonishing.  Mr.  Gott  assured 
me  that  one  of  the  largest  of  them,  containing  upwards 
of  1800  gallons,  when  filled  with  cold  water  from  the  cis- 
tern, requires  no  more  than  half  an  hour  to  heat  it  till 
it  actually  boils  !  By  the  greatest  fire  that  could  be 
made  under  such  a  copper,  it  would  hardly  be  possible 
to  make  it  boil  in  less  than  an  hour. 

It  is  easy  to  perceive  that  the  saving  of  time  which 
will  result  from  the  adoption  of  this  new  mode  of  ap- 
plying heat  will  be  very  great ;  and  it  is  likewise 
evident  that  it  may  be  increased  almost  without  limita- 
tion, merely  by  augmenting  the  diameter  of  the  steam- 
tube.  Care  must,  however,  be  taken,  that  the  boiler  be 
sufficiently  large  to  furnish  the  quantities  of  steam 
required.  The  saving  of  fuel  will  also  be  very  consid- 


336  Of  the  Use  of  Steam 

erable.  Mr.  Gott  informed  me  that,  from  the  best 
calculation  he  had  been  able  to  make,  it  would  amount 
to  near  two  thirds  of  the  quantity  formerly  expended, 
when  each  copper  was  heated  by  a  separate  fire. 

But  these  savings  are  far  from  being  the  only  advan- 
tages that  will  be  derived  from  the  introduction  of  these 
improvements  in  the  management  of  heat.  There  is 
one,  of  great  importance  indeed,  not  yet  mentioned, 
which  alone  would  be  sufficient  to  recommend  the  very 
general  adoption  of  them.  As  the  heat  communicated 
by  steam  can  never  exceed  the  mean  temperature 
of  boiling  water  by  more  than  a  very  few  degrees,  the 
substances  exposed  to  it  can  never  be  injured  by  it. 

In  many  arts  and  manufactures  this  circumstance  will 
be  productive  of  great  advantages,  but  in  none  will  its 
utility  be  more  apparent  than  in  cookery,  and  especially 
in  public  kitchens,  where  great  quantities  of  food  are 
prepared  in  large  boilers  ;  for,  when  the  heat  is  con- 
veyed in  this  manner,  all  the  labour  now  employed  in 
stirring  about  the  contents  of  those  boilers,  to  prevent 
the  victuals  from  being  spoiled  by  burning  to  the  bot- 
toms of  them,  will  be  unnecessary,  and  the  loss  of  heat 
occasioned  by  this  stirring  prevented ;  and,  instead  of 
expensive  coppers  or  metallic  boilers,  which  are  some- 
times unwholesome,  and  always  difficult  to  be  kept  clean, 
and  often  stand  in  need  of  repairs,  common  wooden 
tubs  may,  with  great  advantage,  be  used  as  culinary 
vessels  ;  and  their  contents  may  be  heated  by  portable 
fireplaces,  by  means  of  steam-boilers  attached  to  them. 

As  these  portable  fireplaces  and  their  steam-boilers 
may,  without  the  smallest  inconvenience,  be  made  of 
such  weight,  form,  and  dimensions,  as  to  be  easily 
transported  from  one  place  to  another  by  two  men, 


as  a  Vehicle  for  transporting  Heat.  337 

and  be  carried  through  a  doorway  of  the  common  width, 
with  this  machinery,  and  the  steam-tubes  belonging  to 
it,  and  a  few  wooden  tubs,  a  complete  public  kitchen, 
for  supplying  the  poor  and  others  with  soups  and 
also  with  puddings,  vegetables,  meat,  and  all  other 
kinds  of  food  prepared  by  boiling^  might  be  established 
in  half  an  hour  in  any  room  in  which  there  is  a  chim- 
ney (by  which  the  smoke  from  the  portable  fireplace 
can  be  carried  off);  and  when  the  room  should  be  no 
longer  wanted  as  a  kitchen,  it  might,  in  a  few  minutes, 
be  cleared  of  all  this  culinary  apparatus,  and  made  ready 
to  be  used  for  any  other  purpose. 

This  method  of  conveying  heat  is  peculiarly  well 
adapted  for  heating  baths.  It  is  likewise  highly  probable 
that  it  would  be  found  useful  in  the  bleaching  business 
and  in  washing  linen.  It  would  also  be  very  useful  in 
all  cases  where  it  is  required  to  keep  any  liquid  at  about 
the  boiling-point  for  a  long  time  without  making  it  boil ; 
for  the  quantity  of  heat  admitted  may  be  very  nicely 
regulated  by  means  of  the  brass  cock  belonging  to  the 
steam-tube.  Mr.  Gott  showed  me  a  boiler  in  which 
shreds  of  skins  were  digesting  in  order  to  make  glue,  which 
was  heated  in  this  manner ;  and  in  which  the  heat  was 
so  regulated  that,  although  the  liquid  never  actually 
boiled,  it  always  appeared  to  be  upon  the  very  point 
of  beginning  to  boil. 

This  temperature  had  been  found  to  be  best  calculated 
for  making  good  glue.  Had  any  other  lower  tempera- 
ture been  found  to  answer  better,  it  might  have  been 
kept  up  with  the  same  ease,  and  with  equal  precision, 
by  regulating  properly  the  quantity  of  steam  admitted. 

I  need  not  say  how  much  this  country  is  obliged  to 
Mr.  Gott  and  his  worthy  colleagues.  To  the  spirited 


338  Of  the  Use  of  Steam 

exertions  of  such  men,  who  abound  in  no  other  coun- 
try, we  owe  one  of  the  proudest  distinctions  of  our 
national  character,  that  of  being  an  enlightened  and  an 
enterprising  people. 

In  fitting  up  the  great  kitchen  at  the  house  of  the 
Royal  Institution,  I  availed  myself  of  that  opportunity 
to  show,  in  a  variety  of  different  ways,  how  steam  may 
be  usefully  employed  in  heating  liquids. 

On  one  side  of  the  room,  opposite  to  the  fireplace, 
and  where  there  is  no  appearance  of  any  chimney,  I 
fitted  up  a  steam-boiler,  of  cast-iron,  which,  to  confine 
the  heat,  is  so  completely  covered  up  by  the  brickwork 
in  which  it  is  set,  that  no  part  of  it  is  seen.  This  boiler 
is  supplied  with  water  from  a  reservoir  at  a  distance 
(which  is  not  seen),  and  by  means  of  a  cock,  which  is 
regulated  by  an  hollow  floating  ball  of  thin  copper,  the 
water  in  the  boiler  always  stands  at  the  same  height  or 
level. 

The  steam  from  this  boiler  rises  up  perpendicularly 
in  a  tin  tube,  which  is  concealed  in  a  square  wooden 
tube,  by  the  side  of  the  wall  of  the  room,  and  enters 
an  horizontal  tin  tube  (concealed  in  the  same  manner) 
which  lies  against  the  wall  and  just  under  the  ceiling. 

From  this  horizontal  steam- conduct 'or  three  tubes  de- 
scend perpendicularly  (concealed  in  three  square  wooden 
tubes),  and  enter  three  different  kitchen  boilers  (on  a 
level  with  their  bottoms),  which  are  set  in  brickwork 
against  the  same  side  of  the  room  where  the  steam- 
boiler  is  situated. 

As  each  of  these  boilers  has  its  separate  fireplace, 
properly  furnished  with  a  good  double  door  and  regis- 
ter ash-pit  door,  and  also  with  a  canal,  furnished  with 
a  damper,  for  carrying  off  the  smoke,  either  of  these 


as  a  Vehicle  for  transporting  Heat.  339 

three  boilers  may  be  used  for  cooking,  either  with  a  fire 
made  under  it,  or  with  steam  brought  into  it  from  the 
neighbouring  steam-boiler. 

The  object  I  had  principally  in  view  in  this  arrange- 
ment was  to  show,  in  the  most  striking  and  convincing 
manner,  that  all  the  different  processes  of  cookery 
which  are  performed  by  boiling,  such  as  boiling  meat 
and  vegetables  in  boiling  water,  making  soups,  stew- 
ing, etc.,  may  in  all  cases  be  performed  quite  as  well, 
and  in  many  much  better,  by  heating  the  liquid  which 
is  to  be  boiled,  and  keeping  it  boiling,  by  admitting  hot 
steam  into  it,  than  by  making  a  fire  under  it. 

By  using  one  of  these  boilers  alternately  in  these  two 
ways,  on  different  days,  in  preparing  the  same  kind  of 
food,  I  concluded  that  all  doubts  on  this  subject  would 
be  most  effectually  removed. 

To  exhibit  in  a  manner  still  more  striking  the  appli- 
cation of  steam  to  the  boiling  of  liquids  for  culinary 
purposes,  the  following  arrangement  has  been  made  and 
completed.  A  horizontal  steam-conductor  (concealed 
in  a  square  wooden  tube),  communicating  at  right  angles 
with  the  steam-conductor  before  described,  passes,  just 
below  the  ceiling,  from  the  middle  of  one  side  of  the 
room  to  the  middle  of  the  ceiling,  and  ends  in  a  ves- 
sel in  the  form  of  a  flat  drum,  about  10  inches  in  diame- 
ter and  5  inches  high,  which  is  attached  to  the  ceiling 
perpendicularly  over  the  centre  of  a  large  table  which 
is  placed  in  the  middle  of  the  room. 

On  the  outside  of  this  drum,  or  short  hollow  cylinder 
(which  is  made  of  tin  and  covered  with  wood,  to  con- 
fine the  heat),  there  are,  at  equal  distances,  four  project- 
ing horizontal  tubes,  each  about  i  inch  in  diameter 
and  2  inches  long,  which  communicate  with  the  inside 


340  Of  the  Use  of  Steam 

of  the  drum.  These  tubes  all  point  to  the  same  centre, 
namely,  to  the  centre  of  the  drum. 

To  each  of  these  short  horizontal  tubes  there  is  fixed 
one  end  of  a  steam-tube  composed  of  three  pieces,  fixed 
to  each  other,  and  movable,  by  means  of  joints,  which 
are  all  steam-tight.  • 

The  end  of  this  compound  flexible  steam-tube  is 
united  to  the  end  of  the  short  tube  which  projects  from 
the  side  of  the  drum,  by  means  of  a  steam-joint,  in 
such  a  manner  that  the  steam-tube  attached  to  the 
drum,  and  communicating  with  it,  may  either  be  folded 
up  in  joints  or  lengths  just  under  the  ceiling,  or  it 
may  be  made  to  hang  down  from  the  end  of  the  short 
tube  to  which  it  is  attached.  The  lower  joint,  or 
rather  division,  of  this  flexible  steam-tube,  which  reaches 
nearly  to  the  top  of  the  table,  is  furnished  with  a  brass 
cock,  by  which  it  is  occasionally  closed,  or,  rather,  by 
which  it  is  always  kept  closed  when  it  is  not  in  actual 
use. 

I  might  perhaps  spare  myself  the  trouble  of  describ- 
ing the  manner  in  which  this  culinary  steam-apparatus 
is  used,  as  the  imagination  of  the  reader  will  most  prob- 
ably have  run  before  me.  I  shall,  however,  just  men- 
tion a  very  striking  and  pleasing  manner  of  making  the 
experiment,  in  which  the  action  of  this  machinery  will 
be  exhibited  to  great  advantage. 

If  the  cold  water  which  is  to  be  heated  and  made 
to  boil  by  the  steam  is  put  into  a  large  glass  bowl  or 
jar,  on  plunging  the  lower  end  of  one  of  the  flexible 
steam-tubes  into  the  water,  and  then  opening  the  steam- 
cock,  the  agitation  into  which  the  water  in  the  glass 
vessel  will  be  thrown  will  be  visible  through  the  glass ; 
and  the  passage  of  the  steam,  in  its  elastic  form,  upwards 


as  a  Vehicle  for  transporting  Heat.  341 

through  the  Water  into  the  air,  after  the  water  has  become 
boiling  hot  and  not  before,  will  be  an  instructive,  as  well 
as  an  amusing  experiment. 

Those  of  the  flexible  steam-tubes  which  are  not  in 
actual  use  are  kept  so  folded  up  (in  order  to  their  being 
out  of  the  way)  that  their  two  upper  divisions,  lying 
by  the  side  of  each  other  in  a  horizontal  position,  are 
just  under  the  ceiling  of  the  room  ;  while  their  lower 
divisions  hang  vertically  downwards,  pointing  towards 
the  table. 

In  order  that  the  kitchen  may  not  be  filled  with  steam 
when  any  of  the  boilers  on  the  side  of  the  room  are 
used,  their  covers  are  all  furnished  with  steam-tubes, 
which,  communicating  by  a  particular  contrivance  with 
a  horizontal  steam-tube  which  lies  immediately  over 
these  boilers  just  under  the  ceiling,  and  which,  by  pass- 
ing through  the  wall  of  the  building,  opens  into  the 
external  air,  all  the  waste  steam  from  these  boilers  is 
carried  out  of  the  kitchen. 

Before  I  conclude  this  Essay,  I  shall  add  a  few  obser- 
vations concerning  an  application  of  steam  which  has 
not  yet,  to  my  knowledge,  been  made,  but  which  there 
is  much  reason  to  think  would  turn  out  to  be  of  very 
great  importance  indeed  in  many  cases.  This  is  the  em- 
ploying of  it  for  communicating  degrees  of  heat  above 
that  of  boiling  water. 

I  was  led  to  meditate  on  this  subject  by  an  account  I 
received,  not  long  ago,  of  some  very  surprising  effects 
which  were  produced  in  bleaching,  by  using  the  steam 
of  a  very  strong  solution  of  potash  for  boiling  the  linen, 
instead  of  water  ;  as  I  was  confident  that  no  part  of  the 
alkali  could  possibly  be  evaporated  in  this  process,  I 
could  not  account  in  any  other  way  for  the  effects  pro- 


342  Of  the  Use  of  Steam 

duced,  but  by  supposing  them  to  have  been  owing  to 
the  high  temperature  of  the  steam  which  rose  from  this 
strong  lixivium ;  and  as  steam,  at  a  high  temperature, 
might  easily  be  procured  and  applied  to  the  linen  with- 
out the  use  of  the  alkali,  I  thought  it  would  be  worth 
while  to  try  the  experiment  with  hot  steam  produced 
from  pure  water.  I  mentioned  this  idea  to  Mr.  Duffin, 
Secretary  of  the  Linen  Board  in  Ireland,  who  is  himself 
concerned,  in  an  extensive  way,  in  the  bleaching  business, 
who  has  promised  to  make  some  experiments  on  this 
subject,  which  I  took  the  liberty  to  point  out  and  to 
recommend  to  him  as  being  likely  to  lead  to  interesting 
results. 

Meditating  on  the  various  uses  to  which  hot  or 
(which  is  the  same  thing)  strong  steam  might  be  applied, 
it  occurred  to  me  that  it  would  probably  be  found  to  be 
extremely  useful  in  alum  works,  for  concentrating  the 
liquor  from  which  alum  is  crystallized.  There  are,  as 
is  well  known,  many  difficulties  attending  the  evapora- 
tion and  concentration  of  that  liquid ;  and  it  is  never 
done  without  occasioning  a  very  considerable  expense, 
as  well  for  fuel,  of  which  large  quantities  are  consumed, 
as  also  on  account  of  the  frequent  repairs  of  the  pans, 
which  are  found  to  be  necessary. 

Most,  if  not  all  these  difficulties  might,  I  think,  be 
avoided  by  introducing  strong  steam  into  this  liquor, 
instead  of  concentrating  it  over  a  fire.  This  concen- 
tration might  certainly  be  effected  as  well,  and  probably 
better  and  more  expeditiously,  by  using  hot  steam,  than 
by  the  immediate  use  of  the  heat  of  a  fire,  and  the 
expense  occasioned  by  the  wear  and  tear  of  the  apparatus 
would,  no  doubt,  be  much  less  in  the  former  case  than 
in  the  latter ;  and  if  it  should  be  found  (which  is  not 


as  a  Vehicle  for  transporting  Heat.  343 

unlikely)  that  some  certain  temperature  is  more  advan- 
tageous in  this  process  than  any  other,  that  temperature^ 
when  once  discovered,  may  be  preserved,  with  very  little 
variation,  when  steam  is  used  (by  placing  a  valve,  loaded 
with  a  proper  weight,  in  the  steam-tube,  and  obliging  the 
steam  to  lift  that  valve,  in  order  to  pass  through  the  tube); 
but  there  is  no  possibility  of  regulating,  with  any  pre- 
cision, the  degrees  of  heat  employed  when  liquids  are 
evaporated  in  boilers  over  a  fire. 

I  would  just  point  out  one  more  application  of  steam, 
which,  if  I  am  not  much  mistaken,  will  turn  out  to  be 
very  advantageous  indeed  in  many  respects  ;  —  it  may  be 
employed  in  heating  the  fermented  liquor  from  which 
ardent  spirits  are  distilled. 

A  proposal  for  introducing  watery  vapour  into  a 
liquor  from  which  pure  ardent  spirits  are  to  be  distilled, 
or  forced  away  by  heat,  will,  no  doubt,  be  thought  very 
extraordinary  by  those  who  have  never  meditated  on 
the  subject ;  but  when  they  shall  have  considered  it  with 
attention,  they  will  find  reason  to  conclude  that  this 
method  of  distilling  bids  fair  to  be  very  useful.  The 
saving  of  expense  for  coppers  and  other  costly  utensils 
and  machinery  would  be  very  considerable,  and  the 
danger  of  the  flavour  of  the  spirits  being  injured  by  the 
burning  of  the  liquor  to  the  sides  of  the  copper  would 
be  entirely  removed. 

Steam  has  already  been  introduced,  in  several  great 
manufactories  in  this  country,  into  drying-houses,  and  em- 
ployed with  the  best  effects  for  heating  and  drying  linen, 
cotton,  and  woollen  goods,  after  they  have  been  washed  ; 
it  has  also  been  used  in  the  drying-rooms  of  several  paper- 
manufactories.  When  it  is  used  for  any  of  these  pur- 
poses, it  should  be  introduced  into  tubes  of  large  diam- 


344  Of  tfie  Use  of  Steam,  etc. 

eter,  or  into  several  smaller  tubes,  constructed  of  very 
thin  sheet  copper  (or  into  any  other  metallic  tubes,  hav- 
ing a  large  surface,  that  would  be  cheaper)  ;  and  these 
tubes  should  be  placed  nearly  in  a  horizontal  position 
in  the  lower  part  of  the  drying-room  and  under  the  goods 
that  are  to  be  dried;  and  (in  order  to  economize  the 
heat  as  much  as  possible)  the  water  resulting  from  the 
condensation  of  the  steam  in  the  steam-tubes  should 
be  conducted  by  small  tubes,  well  covered  with  warm 
covering,  into  the  reservoir  which  feeds  the  steam- 
boiler. 

[This  paper  is  printed  from  the  English  edition  of  Rumford's  Es- 
says, Vol.  III.  pp.  475-498.] 


OBSERVATIONS 


RELATIVE    TO 


THE   MEANS   OF   INCREASING    THE    QUANTITIES   OF 
HEAT  OBTAINED  IN  THE  COMBUSTION  OF  FUEL. 

IT  is  a  fact  which  has  been  long  known,  that  clays, 
and  several  other  incombustible  substances,  when 
mixed  with  sea  coal  in  certain  proportions,  cause  the 
coal  to  give  out  more  heat  in  its  combustion  than  it  can 
be  made  to  produce  when  it  is  burned  pure  or  unmixed  ; 
but  the  cause  of  this  increase  of  heat  does  not  appear 
to  have  been  yet  investigated  with  that  attention  which 
so  extraordinary  and  important  a  circumstance  seems  to 
demand. 

Daily  experience  teaches  us  that  all  bodies  —  those 
which  are  incombustible,  as  well  as  those  which  are 
combustible  and  actually  burning  —  throw  off  in  all 
directions  heat,  or  rather  calorific  (heat-making)  rays, 
which  generate  heat  wherever  they  are  stopped  or  ab- 
sorbed; but  common  observation  was  hardly  sufficient 
to  show  any  perceptible  difference  between  the  quanti- 
ties of  calorific  rays  thrown  off  by  different  bodies,  when 
heated  to  the  same  temperature  or  exposed  in  the 
same  fire,  although  the  quantities  so  thrown  off  might 
be,  and  probably  are,  very  different. 

It  has  lately  been  ascertained,  that,  when  the  sides  and 
back  of  an  open  chimney  fireplace  in  which  coals  are 
burned  are  composed  of  firebricks,  and  heated  red-hot, 


346      Means  of  increasing  the  Quantities  of  Heat 

they  throw  off  into  the  room  incomparably  more  heat 
than  all  the  coals  that  could  possibly  be  put  into  the 
grate,  even  supposing  them  to  burn  with  the  greatest 
possible  degree  of  brightness.  Hence  it  appears  that  a 
red-hot  burning  coal  does  not  send  off  near  so  many 
calorific  rays  as  a  piece  of  red-hot  brick  or  stone  of  the 
same  form  and  dimensions ;  and  this  interesting  dis- 
covery will  enable  us  to  make  very  important  improve- 
ments in  the  construction  of  our  fireplaces,  and  also  in 
the  management  of  our  fires. 

The  fuel,  instead  of  being  employed  to  heat  the  room 
directly  or  by  the  direct  rays  from  the  fire,  should  be  so 
disposed  or  placed  as  to  heat  the  back  and  sides  of  the 
grate,  which  must  always  be  constructed  of  firebrick 
or  firestone,  and  never  of  iron  or  of  any  other  metal. 
Few  coals,  therefore,  when  properly  placed,  make  a 
much  better  fire  than  a  larger  quantity,  and  shallow 
grates,  when  they  are  constructed  of  proper  materials, 
throw  more  heat  into  a  room,  and  with  a  much  less 
consumption  of  fuel,  than  deep  grates  ;  for  a  large  mass 
of  coals  in  the  grate  arrests  the  rays  which  proceed  from 
the  back  and  sides  of  the  grate,  and  prevents  their  com- 
ing into  the  room  ;  or,  as  fires  are  generally  managed, 
it  prevents  the  back  and  sides  of  the  grate  from  ever 
being  sufficiently  heated  to  assist  much  in  heating  the 
room,  even  though  they  be  constructed  of  good  materi- 
als and  large  quantities  of  coals  be  consumed  in  them. 

It  is  possible,  however,  by  a  simple  contrivance,  to 
make  a  good  and  an  economical  fire  in  almost  any  grate, 
though  it  would  always  be  advisable  to  construct  fire- 
places on  good  principles,  or  to  improve  them  by 
judicious  alterations,  rather  than  to  depend  on  the  use 
of  additional  inventions  for  correcting  their  defects. 


obtained  in  the  Combustion  of  Fuel.  347 

To  make  a  good  fire  in  a  bad  grate,  the  bottom  of 
the  grate  must  be  first  covered  with  a  single  layer  of 
balls,  made  of  good  firebricks  or  artificial  firestone,  well 
burned,  each  ball  being  perfectly  globular,  and  about 
2-J  or  2-|  inches  in  diameter.  On  this  layer  of  balls 
the  fire  is  to  be  kindled,  and,  in  filling  the  grate,  more 
balls  are  to  be  added  with  the  coals  that  are  laid  on  ; 
care  must,  however,  be  taken  in  this  operation  to  mix 
the  coals  and  the  balls  well  together,  otherwise,  if  a 
number  of  the  balls  should  get  together  in  a  heap,  they 
will  cool,  not  being  kept  red-hot  by  the  combustion  of 
the  surrounding  fuel,  and  the  fire  will  appear  dull  in 
that  part;  but  if  no  more  than  a  due  proportion  of  the 
balls  are  used,  and  if  they  are  properly  mixed  with  the 
coals,  they  will  all,  except  it  be  those  perhaps  at  the 
bottom  of  the  grate,  become  red-hot,  and  the  fire  will 
not  only  be  very  beautiful,  but  it  will  send  off  a  vast 
quantity  of  radiant  heat  into  the  room,  and  will  con- 
tinue to  give  out  heat  for  a  great  length  of  time.  It  is 
the  opinion  of  several  persons  who  have  for  a  consid- 
erable time  practised  this  method  of  making  their  fires, 
that  more  than  one  third  of  the  fuel  usually  consumed 
may  be  saved  by  this  simple  contrivance.  It  is  very 
probable  that,  with  careful  and  judicious  management, 
the  saving  would  amount  to  one  half,  or  fifty  per  cent. 

As  these  balls,  made  in  moulds  and  burnt  in  a  kiln, 
would  cost  very  little,  and  as  a  set  of  them  would  last 
a  long  time,  —  probably  several  years,  —  the  saving  of 
expense  in  heating  rooms  by  chimney  fires  with  bad 
grates,  in  this  way,  is  obvious  ;  but  still,  it  should  be 
remembered  that  a  saving  quite  as  great  may  be  made 
by  altering  the  grate,  and  making  it  a  good  fireplace. 

In  using  these  balls,  care  must  be  taken  to  prevent 


348      Means  of  increasing  the  Quantiti.s  of  Heat 

their  accumulating  at  the  bottom  of  the  grate.  As  the 
coals  go  on  to  consume,  the  balls  mixed  with  them  will 
naturally  settle  down  towards  the  bottom  of  the  grate, 
and  the  tongs  must  be  used  occasionally  to  lift  them  up  ; 
and  as  the  fire  grows  low,  it  will  be  proper  to  remove 
a  part  of  them,  and  not  to  replace  them  in  the  grate 
till  more  coals  are  introduced.  A  little  experience  will 
show  how  a  fire  made  in  this  manner  can  be  managed 
to  the  greatest  advantage  and  with  the  least  trouble. 

Balls  made  of  pieces  of  any  kind  of  well-burned  hard 
brick,  though  not  equally  durable  with  firebrick,  will 
answer  very  well,  provided  they  be  made  perfectly 
round  ;  but  if  they  are  not  quite  globular,  their  flat  sides 
will  get  together,  and  by  obstructing  the  free  passage  of 
the  air  amongst  them  and  amongst  the  coals  will  pre- 
vent the  fire  from  burning  clear  and  bright. 

The  best  composition  for  making  these  balls,  when 
they  are  formed  in  moulds  and  afterwards  dried  and 
burned  in  a  kiln,  is  pounded  crucibles  mixed  up  with 
moistened  Sturbridge  clay  ;  but  good  balls  may  be  made 
with  any  very  hard  burned  common  bricks,  reduced  to  a 
coarse  powder,  and  mixed  with  Sturbridge  clay,  or  even 
with  common  clay.  The  balls  should  always  be  made 
so  large  as  not  to  pass  through  between  the  front  bars 
of  a  grate. 

These  balls  have  one  advantage,  which  is  peculiar  to 
them,  and  which  might  perhaps  recommend  the  use  of 
them  to  the  curious,  even  in  fireplaces  constructed  on 
the  best  principles  :  they  cause  the  cinders  to  be  con- 
sumed almost  entirely ;  and  even  the  very  ashes  may 
be  burned,  or  made  to  disappear,  if  care  be  taken  to 
throw  them  repeatedly  upon  the  fire  when  it  burns  with 
an  intense  heat.  It  is  not  difficult  to  account  for  this 


obtained  in  the  Combustion  of  Fuel.  349 

effect  in  a  satisfactory  manner,  and  in  accounting  for  it 
we  shall  explain  a  circumstance  on  which  it  is  probable 
that  the  great  increase  of  the  heat  of  an  open  fire  where 
these  balls  are  used  may  in  some  measure  depend. 
The  small  particles  of  coal  and  of  cinder  which  in  a 
common  fire  fall  through  the  bottom  of  the  grate  and 
escape  combustion,  when  these  balls  are  used  can  hardly 
fail  to  fall  and  lodge  on  some  of  them ;  and  as  they 
are  intensely  hot,  these  small  bodies  which  alight  upon 
them  in  their  fall  are  soon  heated  red-hot,  and  disposed 
to  take  fire  and  burn  ;  and  as  fresh  air  from  below  the 
grate  is  continually  making  its  way  upwards  amongst 
the  balls,  every  circumstance  is  highly  favourable  to  the 
rapid  and  complete  combustion  of  these  small  inflam- 
mable bodies.  But  if  these  small  pieces  of  coal  and 
cinder  should,  in  their  fall,  happen  to  alight  upon  the 
metallic  bars  which  form  the  bottom  of  the  grate,  as 
these  bars  are  conductors  of  heat,  and,  on  account  of 
that  circumstance,  as  well  as  of  their  situation, — below 
the  fire,  —  never  can  be  made  very  hot,  any  small 
particle  of  fuel  that  happens  to  come  into  contact  with 
them  not  only  cannot  take  fire,  but  would  cease  to  burn, 
should  it  arrive  in  a  state  of  actual  combustion. 

These  facts  are  very  important,  and  well  deserving  of 
the  attention  of  those  who  may  derive  advantage  from 
the  improvement  of  fireplaces  and  the  economy  of  fuel. 

There  are  some  circumstances  w.hich  strongly  indicate 
that  an  admixture  of  incombustible  bodies  with  fuel, 
and  especially  with  coal,  causes  an  increase  of  the  heat, 
even  when  the  fuel  is  burned  in  a  closed  fireplace.  No 
fireplace  can  well  be  contrived  more  completely  closed 
than  those  of  the  iron  stoves  in  common  use  in  the 
Netherlands ;  but  in  these  stoves,  which  are  heated 


350      Means  of  increasing  the  Quantities  of  Heat 

by  coal  fires,  a  large  proportion  of  wet  clay  is  always 
coarsely  mixed  with  the  coals  before  they  are  introduced 
into  the  fireplace.  If  this  practice  had  not  been  found 
to  be  useful,  it  would  certainly  never  have  obtained  gen- 
erally, nor  would  it  have  been  continued,  as  it  has 
been,  for  more  than  two  hundred  years. 

The  combination  of  different  substances,  combus- 
tible and  incombustible,  to  form,  artificially,  various 
kinds  of  cheap  and  pleasant  fuel,  particularly  adapted 
for  the  different  processes  in  which  the  fuel  is  employed, 
is  a  subject  well  worthy  of  the  attention  of  enterprising 
and  ingenious  men. ,  How  much  excellent  fuel,  for 
instance,  might  be  made  with  proper  additions  and 
proper  management,  of  the  mountains  of  refuse  coal- 
dust  that  lie  useless  at  the  mouths  of  coal-pits  ;  and 
how  much  would  it  contribute  to  cleanliness  and  ele- 
gance if  the  use  of  improved  coke,  or  of  hard  and  light 
fire-balls,  could  be  generally  introduced  in  our  houses 
and  kitchens,  instead  of  crude,  black,  powdery,  dirty 
sea  coal !  Of  the  great  economy  that  would  result  from 
such  a  change  there  cannot  be  the  smallest  doubt. 

It  is  a  melancholy  truth,  but  at  the  same  time  a  most 
indisputable  fact,  that,  while  the  industry  and  ingenuity 
of  millions  are  employed,  with  unceasing  activity,  in 
inventing,  improving,  and  varying  those  superfluities 
which  wealth  and  luxury  introduce  into  society,  no 
attention  whatever  is  paid  to  the  improvement  of  those 
common  necessaries  of  life  on  which  the  subsistence 
of  all,  and  the  comforts  and  enjoyments  of  the  great 
majority  of  mankind,  absolutely  depend. 

Much  will  be  done  for  the  benefit  of  society,  if  means 
can  be  devised  to  call  the  attention  of  the  active  and 
benevolent  to  this  long-neglected,  but  most  interesting 
subject. 


obtained  in  the  Combustion  of  Fuel.  351 

The  Royal  Institution  seems  to  be  well  calculated  to 
facilitate  and  expedite  the  accomplishment  of  this  im- 
portant object.  Indeed,  it  is  more  than  probable  that 
this,  precisely,  is  the  object  which  was  principally  had 
in  view  in  the  foundation  and  arrangement  of  that 
establishment. 

[This  paper  is  printed  from  the  Journals  of  the  Royal  Institution  of 
Great  Britain,  I.  (1802),  pp.  28-33.] 


DESCRIPTION   OF   A   NEW    BOILER, 


CONSTRUCTED 


WITH     A     VIEW     TO     THE    SAVING     OF    FUEL. 

IT  is  well  known  that  much  is  gained  in  the  saving  of 
fuel,  when  an  extensive  surface  is  given  to  that  part 
of  the  boiler  against  which  the  flame  strikes;  but  this  ad- 
vantage is  often  counterbalanced  by  great  inconveniences. 
For  a  boiler  of  the  form  usually  employed,  having  the 
bottom  very  much  extended  in  proportion  to  its  ca- 
pacity, must  necessarily  present  a  great  surface  to  the  at- 
mosphere, and  the  loss  of  heat,  occasioned  by  the  cold 
air  coming  in  contact  with  this  surface,  may  be  more 
than  sufficient  to  compensate  the  advantage  derived  from 
the  extended  surface  of  the  bottom.  And  where  the 
boiler  is  employed  for  producing  steam,  as  it  is  indis- 
pensably necessary  that  it  should  be  of  a  thickness  suf- 
ficient to  resist  the  expansive  force  of  the  steam,  it  is 
evident  that,  if  the  diameter  be  augmented  (with  a  view 
to  increase  the  surface  of  the  bottom),  a  considerable  ex- 
pense is  incurred  on  account  of  the  additional  strength 
that  must  be  given  to  the  sides. 

Having  been  engaged  in  the  year  1796  in  a  set  of  ex- 
periments in  which  I  employed  the  steam  of  boiling 
water  as  a  vehicle  of  heat,  I  had  a  boiler  made  for  this 
purpose,  on  a  new  construction,  which  answered  well, 
and  even  beyond  my  expectations ;  and  as  this  boiler 
might  be  used  with  advantage  in  many  cases,  even  where 


Description  of  a  new  Boiler,  etc.  353 

it  is  only  required  to  heat  liquids  in  an  open  boiler, 
this,  and  another  motive,  which  it  would  be  useless  to 
mention  in  this  place,  have  lately  induced  me  to  con- 
struct one  here  (at  Paris)  and  to  present  it  to  the  In- 
stitute. 

The  object  chiefly  had  in  view  in  the  construction  of 
this  boiler  was  to  give  it  such  a  form,  that  the  surface 
exposed  to  the  fire  should  be  great  in  comparison  with 
its  diameter  and  capacity  ;  and  this  without  having  a 
great  surface  exposed  to  the  cold  air  of  the  atmosphere. 

The  body  of  the  boiler  is  in  the  shape  of  a  drum.  It 
is  a  vertical  cylinder  of  copper  12  inches  in  diameter  and 
12  inches  high,  closed  at  top  and  at  bottom  by  circular 
plates. 

In  the  centre  of  the  upper  plate  there  is  a  cylindrical 
neck  6  inches  in  diameter  and  3  inches  high,  shut  at 
top  by  a  plate  of  copper  3  inches  in  diameter  and  3 
lines  in  thickness,  fastened  down  by  screws. 

This  last  plate  is  pierced  by  three  holes,  each  about 
5  lines  in  diameter.  The  first,  which  is  in  the  centre 
of  the  plate,  receives  a  vertical  tube,  which  conveys 
water  to  the  boiler  from  a  reservoir,  which  is  placed 
above.  This  tube,  which  descends  in  the  inside  of  the 
boiler  to  within  an  inch  above  the  circular  plate  which 
forms  its  bottom,  has  a  cock  near  its  lower  end.  This 
cock  is  alternately  opened  and  shut,  by  means  of  a  float- 
er which  swims  on  the  surface  of  the  water  contained  in 
the  body  of  the  boiler. 

The  second  of  the  holes  in  the  plate  that  closes  the 
neck  of  the  boiler  receives  the  lower  end  of  another 
vertical  tube,  which  serves  to  convey  the  steam  from 
the  boiler  to  the  place  where  it  is  to  be  used. 

The  third  hole  is  occupied  by  a  safety-valve. 

VOL.  ii.  23 


354        Description  of  a  new  Boiler,  constructed 

This  description  shows  that  there  is  nothing  new  in 
the  construction  or  arrangement  of  the  upper  part  of 
this  boiler.  In  its  lower  part  there  is  a  contrivance  for 
increasing  its  surface,  which  has  been  found  very  useful. 

The  flat  circular  bottom  of  the  body  of  the  boiler, 
which,  as  I  said  before,  is  12  inches  in  diameter,  being 
pierced  by  seven  holes,  each  3  inches  in  diameter,  seven 
cylindrical  tubes  of  thin  sheet-copper,  3  inches  in  diam- 
eter and  9  inches  long,  closed  below  by  circular  plates, 
are  fixed  in  these  holes,  and  firmly  riveted,  and  then 
soldered  to  the  flat  bottom  of  the  boiler. 

On  opening  the  communication  between  the  boiler 
and  its  reservoir,  the  water  first  fills  the  seven  tubes, 
and  then  rises  to  the  cylindrical  body  of  the  boiler  ;  but 
it  can  never  rise  above  6  inches  in  the  body  of  the 
boiler,  for  when  it  has  got  to  that  height,  the  floater  is 
lifted  to  the  height  necessary  for  shutting  the  cock  that 
admits  the  water. 

When  the  height  of  the  water  in  the  boiler  is  dimin- 
ished a  few  lines  by  the  evaporation,  the  floater  descends 
a  little,  the  cock  is  again  opened,  and  the  water  flows  in 
again  from  the  reservoir. 

As  the  seven  tubes  that  descend  from  the  flat  bottom 
of  the  body  of  this  boiler  into  the  fireplace  are  sur- 
rounded on  all  sides  by  the  flame,  the  liquid  contained 
in  the  boiler  is  heated,  and  made  to  boil  in  a  short  time, 
and  with  the  consumption  of  a  relatively  small  quan- 
tity of  fuel  ;  and  when  the  vertical  sides  of  the  body 
of  the  boiler  and  its  upper  part  are  suitably  enveloped, 
in  order  to  prevent  the  loss  of  heat  by  these  surfaces, 
this  apparatus  may  be  employed  with  much  advantage 
in  all  cases  where  it  is  required  to  boil  water  for  procur- 
ing steam. 


with  a  View  to  the  Saving  of  Fuel.  355 

And  as  in  the  case  where  the  boiler  is  constructed  on 
a  great  scale,  the  seven  tubes  that  descend  from  the  bot- 
tom of  the  boiler  into  the  fire  may  be  made  of  cast-iron, 
whilst  the  body  of  the  boiler  is  composed  of  sheet-iron 
or  sheet-copper,  it  is  certain  that  a  boiler  of  this  kind, 
sufficiently  large  for  a  steam-engine,  a  dyeing-house,  or 
a  spirit-distillery,  would  cost  much  less  than  a  boiler  of 
the  usual  form,  of  equal  surface  and  power. 

But  in  all  cases  where  it  is  required  to  produce  a  great 
quantity  of  steam,  it  will  be  always  preferable  to  em- 
ploy several  boilers  of  a  middling  size,  placed  beside 
each  other,  and  heated  each  by  a  separate  fire,  instead 
of  using  one  large  boiler  heated  by  one  fire. 

I  have  shown  in  my  Sixth  Essay,  on  the  management 
of  fire  and  the  economy  of  fuel,  that  beyond  a  certain 
limit  there  is  no  advantage  derived  from  augmenting 
the  capacity  of  a  boiler. 

It  will  be  perceived  that  the  boiler  which  I  have  the 
honour  of  presenting  to  this  Society  is  of  a  form  fit  for 
being  placed  in  a  portative  furnace,  and  it  was  actually 
intended  for  that  purpose. 

Its  furnace,  which  is  made  of  bricks,  with  a  circular 
iron  grate  of  6  inches  in  diameter,  is  built  in  the  inside 
of  a  cylinder  of  sheet-iron,  17  inches  in  diameter  and  3 
feet  high,  and  can  be  easily  transported  from  place  to 
place  by  two  men. 

This  cylinder  of  sheet-iron,  which  is  divided  into 
two  parts,  in  order  to  facilitate  the  construction  of  the 
masonry,  weighs  only  forty-six  pounds.  The  masonry 
weighs  about  a  hundred  and  fifty  pounds,  and  the  boiler 
twenty-two  pounds. 

In  order  to  form  an  estimate  of  the  advantage  which 
the  particular  form  of  this  boiler  gives  it  in  accelerating 


356       Description  of  a  new  Boiler,  constrticted 

its  heating,  we  may  compare  the  extent  of  surface  that 
it  presents  to  the  action  of  the  fire  with  that  of  the  flat 
bottom  of  a  common  boiler. 

The  diameter  of  the  bottom  of  a  cylindrical  boiler 
being  12  inches,  the  surface  is  113.88  square  inches; 
but  the  surface  of  the  sides  of  the  seven  tubes  that  de- 
scend from  the  flat  bottom  of  our  boiler  (which  is  like- 
wise 12  inches  in  diameter)  is  593.76  square  inches. 
Therefore  the  new  boiler  has  a  surface  exposed  to  the 
direct  action  of  the  fire,  more  than  five  times  greater 
than  that  of  a  boiler  of  equal  diameter  and  of  the  ordi- 
nary form ;  how  much  this  difference  must  affect  the 
celerity  of  heating  is  easy  to  conceive. 

In  the  manner  in  which  boilers  are  usually  set,  their 
vertical  sides  are  but  little  struck  by  the  flame,  and  on 
that  account  I  have  not  taken  the  effect  of  the  sides  into 
consideration  in  my  estimate ;  but  even  taking  them 
into  account,  the  new  boiler  will  always  have  a  surface 
exposed  to  the  fire  at  least  twice  as  great  as  that  of  a 
common  cylindrical  boiler  of  the  same  diameter,  as  can 
easily  be  shown. 

The  new  boiler  being  12  inches  in  diameter  and  12 
inches  high,  and  each  of  its  seven  tubes  being  3  inches 
in  diameter  and  9  inches  high,  its  surface  is  1160.44 
square  inches,  without  reckoning  the  circular  plate  that 
closes  its  top,  nor  its  neck. 

The  surface  of  the  bottom  and  sides  of  a  cylindrical 
boiler  of  12  inches  in  diameter  and  12  inches  high  will 
be  566.68  square  inches. 

As  the  quantity  of  heat  that  enters  a  boiler  in  a  given 
time  is  in  proportion  to  the  extent  of  surface  that  the 
boiler  presents  to  the  fire,  it  is  evident  that,  other 
circumstances  being  the  same,  a  .boiler  with  tubes  de- 


with  a  View  to  the  Saving  of  Fuel.  357 

scending  from  its  bottom  will  be  heated  at  least  twice 
as  soon  as  a  cylindrical  boiler  of  the  same  diameter  with 
a  flat  bottom. 

In  order  that  a  cylindrical  boiler  with  flat  bottom, 
surrounded  by  flame  on  all  sides,  might  have  the  same 
extent  of  surface  exposed  to  the  fire  as  a  boiler  with 
tubes,  it  would  be  necessary  to  give  it  a  diameter  greater 
than  that  of  the  boiler  with  tubes  in  the  proportion  of 
the  square  root  of  1 160.44  t°  the  square  root  of  566.68, 
that  is,  of  17.171  to  12. 

Therefore,  in  order  that  a  cylindrical  boiler  with  a 
flat  bottom  might  have  the  same  extent  of  surface  ex- 
posed to  the  fire  as  our  boiler  with  tubes  of  12  inches 
in  diameter,  it  would  be  necessary  to  give  it  a  diameter 
of  17.171  inches. 

But  if  the  diameter  of  a  boiler  intended  for  pro- 
ducing steam  be  increased,  it  is  necessary,  at  the  same 
time,  to  increase  its  thickness,  in  order  to  increase  its 
strength. 

The  necessary  increase  of  thickness,  and  the  expense 
that  it  will  occasion,  can  be  easily  calculated. 

The  effort  that  an  elastic  fluid  exerts  against  the  sides 
of  the  containing  vessel  is  in  proportion  to  the  surface 
of  a  longitudinal  and  central  section  of  the  vessel,  and 
consequently  in  proportion  to  the  square  of  its  diameter, 
the  form  remaining  the  same.  Hence  we  may  conclude, 
that  a  steam-boiler  of  a  cylindrical  form  with  a  flat  bot- 
tom, which  has  the  same  extent  of  surface  exposed  to 
the  fire  as  a  boiler  of  12  inches  in  diameter  with  tubes, 
should  be  at  least  twice  as  thick  as  this  last,  in  order 
to  have  an  equal  degree  of  strength  for  resisting  the 
expansive  power  of  the  steam. 

The  boiler  which  I  have  the  honour  of  presenting  to 


358  Description  of  a  new  Boiler,  etc. 

the  Society  is  particularly  intended  to  serve  as  a  steam- 
boiler,  but  it  may  undoubtedly  be  applied  to  other  pur- 
poses. Having  shown  it  to  M.  Auzilly,  son  of  a  con- 
siderable soap-manufacturer  of  Marseilles,  he  thought 
that  it  might  be  employed  with  advantage  in  the  making 
of  soap ;  and  from  what  he  told  me  of  the  process,  and 
of  the  boilers  employed  in  that  art,  I  am  persuaded 
that  the  experiment  would  succeed  perfectly. 

But,  after  all,  it  remains  to  be  determined  whether  it 
would  not  be  still  more  advantageous  to  employ  steam 
as  a  vehicle  of  heat  in  the  making  of  soap,  instead  of 
lighting  the  fire  under  the  bottom  of  the  vessel  in  which 
the  soap  is  made. 

The  result  of  an  experiment  which  we  are  to  make, 
M.  Auzilly  and  myself,  will  probably  throw  some  light 
upon  this  question. 

[This  paper  is  printed  from  Nicholson's  Journal,  XVII.  (1807), 
pp.  5-10.] 


EXPERIMENT 


USE  OF  THE   HEAT  OF  STEAM,   IN  PLACE  OF  THAT 
OF  AN  OPEN  FIRE,  IN  THE  MAKING  OF  SOAP. 

I  HAD  the  honour  of  announcing  to  this  Assembly, 
at  the  last  meeting  but  one,  that  M.  Auzilly  a'nd 
myself  were  to  make  an  experiment  on  the  use  of  steam 
in  the  making  of  soap.  This  experiment  we  have 
made,  and  with  perfect  success. 

I  have  the  honour  to  lay  before  the  Society  a  piece 
of  soap  of  about  ten  cubic  inches,  made  in  my  labora- 
tory by  this  new  process,  which  required  only  six  hours 
of  boiling,  whereas  sixty  hours  and  more  are  necessary 
in  the  ordinary  method  of  making  soap. 

From  all  the  appearances  that  we  observed  in  the 
course  of  this  experiment,  and  from  its  results,  we 
think  ourselves  authorized  to  conclude  that  this  new 
method  of  making  soap  cannot  fail  to  be  advantageous  in 
every  respect,  and  that  it  will  soon  be  generally  adopted. 

We  propose  to  repeat  the  experiment  on  a  larger 
scale,  as  soon  as  we  shall  be  able  to  procure  the  neces- 
sary utensils,  and  we  beg  the  Society  to  appoint  com- 
missioners to  be  present  during  its  execution. 

As  I  intend  to  communicate  to  the  Institute,  upon  a 
future  occasion,  all  the  details  of  our  experiment,  with 
an  account  of  the  apparatus  we  employed  in  it,  I  shall 


360  On  the  Use  of  the  Heat  of  Steam, 

for  the  present  make  only  one  observation  on  the  prob- 
able cause  of  the  acceleration  of  the  formation  of  soap, 
which  we  observed.  I  believe  that  this  acceleration  is 
due  in  great  measure,  if  not  entirely,  to  a  motion  of  a 
peculiar  kind  in  the  mixture  of  oil  and  lye,  occasioned 
by  the  sudden  condensation  of  the  steam  introduced 
into  the  liquor.  It  is  a  sharp  stroke,  like  that  of  a 
hammer,  which  made  the  whole  apparatus  tremble. 

These  strokes,  which  succeeded  rapidly  in  certain  cir- 
cumstances, and  which  were  violent  enough  to  be  heard 
at  a  considerable  distance,  must  necessarily  have  forced 
the  particles  of  oil  and  alkali  to  approach  each  other, 
and  consequently  to  unite. 

As  the  violence  of  these  strokes  diminished  greatly  as 
soon  as  the  liquid  had  acquired  nearly  the  temperature 
of  the  steam,  I  propose  to  supply  this  defect  by  a  par- 
ticular arrangement  of  the  apparatus  in  the  experiment 
we  are  going  to  make.  I  shall  divide  the  vessel  into 
two  parts,  by  a  horizontal  diaphragm  of  thin  sheet  cop- 
per, and,  causing  a  slow  current  of  cold  water  to  pass 
through  the  lower  division  or  compartment  of  the  ves- 
sel, I  shall  introduce  steam  into  it,  through  a  particular 
tube  destined  for  that  purpose,  as  soon  as  the  mixture 
of  oil  and  alkali  which  occupies  the  upper  division  of 
the  vessel  is  become  too  hot  for  condensing  the  steam. 

The  steam  which  enters  the  water  (always  kept  cold) 
that  fills  the  lower  compartment  of  the  vessel  will  be 
condensed  suddenly,  and  the  sharp  strokes  which  result 
will  be  communicated  through  the  thin  diaphragm  to 
the  hot  liquid  contained  in  the  upper  division  of  the 
vessel,  and  will,  I  expect,  accelerate  the  union  of  the 
oil  with  the  alkali.  I  shall  then  shut  almost  entirely 
the  cock  which  admits  steam  into  the  upper  division  of 


in  place  of  an  open  Fire,  in  making  Soap.      361 

the  vessel,  in  order  to  prevent  a  useless  consumption 
of  steam  and  heat. 

I  shall  not  fail  to  give  an  account  of  the  results  of 
this  new  experiment  to  this  Assembly  ;  and  I  shall  re- 
joice if  by  any  researches  I  shall  be  so  happy  as  to  con- 
tribute to  the  improvement  of  an  art  which  is  undoubt- 
edly of  great  importance  to  society. 

[This  paper  is  printed  from  Nicholson's  Journal,  XVII.  (1807), 
pp.  10-  12.] 


ACCOUNT 


NEW   EXPERIMENTS   ON  WOOD   AND   CHARCOAL. 

HAVING  had  occasion  to  dry  several  kinds  of 
wood,  to  ascertain  how  much  water  was  con- 
tained in  them,  I  procured  a  piece  of  each  kind  six 
inches  long  and  half  an  inch  thick,  and  planed  off  some 
pretty  thin  shavings,  which  I  kept  to  dry  for  eight  days 
in  a  room,  the  temperature  of  which  was  constantly 
about  60°  F.  The  wood  had  been  previously  drying 
two  or  three  years  in  a  joiner's  workshop. 

Of  each  kind  of  shavings  I  took  10  grammes  (154.5 
grains),  which  I  placed  on  a  china  plate  in  a  kind  of 
stove  made  of  sheet-iron,  and  heated  them  moderately 
by  a  small  fire  under  the  stove  for  twelve  hours,  after 
which  they  were  suffered  to  cool  gradually  during 
twelve  hours  more.  The  stove,  being  surrounded  with 
brickwork,  was  still  hot  twelve  hours  after  the  fire  had 
been  extinguished. 

On  taking  out  the  china  plates  in  succession  and 
weighing  the  shavings  anew,  their  weight  was  found  to 
be  diminished  about  one  tenth,  some  a  little  more, 
others  a  little  less.  When  the  shavings  were  put  into 
the  stove,  their  weight  was  10  grammes  ;  when  taken 
out,  it  was  about  9.  Their  colour  was  not  perceptibly 
altered,  and  they  had  no  appearance  of  having  been  ex- 
posed to  a  strong  heat. 


Account  of  some  new  Experiments,  etc.         363 

Desirous  of  knowing  how  far  the  drying  of  wood 
might  be  carried,  I  replaced  them  all  in  the  stove,  which 
I  heated  as  before,  neither  more  nor  less,  for  twelve 
hours,  and  afterward  left  to  cool  slowly  for  twelve 
hours. 

On  taking  out  the  shavings  the  next  day,  they  had  all 
changed  colour  more  or  less ;  from  a  yellowish-white 
they  had  become  light  brown,  dark  brown,  more  or  less 
yellow,  and  some  of  a  fine  purple. 

Their  weight,  which  was  at  first  10  grammes,  was  now 
found  to  be 

Oak    .         .         .         .7.16  Cherry        .         .         .  8.60 

Elm  .         .         .  8.18  Linden             .         .  7.86 

Beech           ...  8.59                       -    (after    having 

Maple  .         .         .  8.41                been  in  the  open  air 

Ash     ....  8.40                twenty-four  hours)  .  8.06 

Birch  .         .         .  7.40  Male  fir .         .         .  8.46 

Service        .         .         .  8.46  Female  fir  .         .         .  8.66 

Wishing  to  know  whether  the  wood  might  not  be 
reduced  to  charcoal  by  continuing  the  moderate  heat  of 
the  stove  a  long  time,  I  took  half  the  linden  shavings, 
which  weighed  4.03  grarnmes,  placed  them  in  a  china 
saucer  supported  by  a  cylindrical  earthen  vessel  3  inches 
in  diameter  and  4  inches  high,  put  this  on  an  earthen 
plate,  and  covered  it  by  a  glass  jar  6  inches  in  diameter 
and  8  inches  high.  On  the  earthen  plate  was  a  layer  of 
ashes  about  an  inch  deep,  serving  to  close  the  mouth  of 
the  jar  slightly. 

This  little  apparatus  being  placed  in  the  stove,  it  was 
heated  a  third  time  for  twelve  hours,  and  then  left 
twelve  hours  without  fire,  to  cool  gradually. 

On  taking  out  the  apparatus,  I  found  that  the  wood 


364  Account  of  some  new  Experiments 

was  become  perfectly  black,  and  that  the  glass  jar  was 
yellowish,  and  its  transparency  diminished. 

On  weighing  the  shavings,  which  retained  their  origi- 
nal figure  completely,  I  was  surprised  to  find  that  they 
weighed  only  2.21  grammes.  As  they  were  the  remains 
of  5  grammes  of  wood,  and  as,  from  the  experiments 
of  Messrs.  Gay-Lussac  and  Thenard,  I  had  expected  to 
find  in  this  wood  at  least  fifty  per  cent  of  charcoal,  I  did 
not  think  it  possible  to  reduce  the  weight  of  the  shav- 
ings to  less"  than  2.5  grammes,  particularly  with  the 
moderate  heat  I  employed. 

To  clear  up  my  doubts,  I  replaced  the  apparatus 
in  the  stove,  and  heated  it  again  as  before  for  twelve 
hours,  and  afterwards  left  it  in  the  stove  twelve  hours 
to  cool. 

On  taking  out  the  apparatus,  I  found  that  the  shav- 
ings weighed  only  1.5  grammes.  The  jar  was  less  trans- 
parent, and  of  a  blackish-yellow  colour  throughout,  but 
particularly  in  its  upper  part,  above  the  level  of  the 
brim  of  the  saucer  in  which  the  shavings  were.  These 
shavings  were  still  of  a  perfect  black. 

Having  heated  the  apparatus  again  for  twelve  hours, 
and  then  left  it  to  cool,  I  was  surprised,  on  taking  it  out 
of  the  stove  the  next  day,  to  find  that  the  jar  had  again 
become  clear  and  transparent.  Not  the  least  trace  of 
the  yellow  coating  with  which  its  inner  surface  had  been 
covered  now  remained. 

On  examining  the  wood,  I  found  that  this  also  had 
changed  its  colour.  It  had  assumed  a  bluish  hue, 
pretty  deep,  but  very  different  from  the  decided  black  it 
had  before.  Its  weight  was  1.02  grammes. 

I  put  it  twice  more  into  the  stove,  and  each  time  its 
weight  was  diminished,  so  that  the  5  grammes  of  wood 


on  Wood  and  Charcoal.  365 

were  reduced  at  last  to  0.27  of  a  gramme,  or  about  a 
twentieth  of  the  original  weight. 

I  am  persuaded  that  I  should  have  diminished  it  still 
more,  if  I  had  continued  the  experiment  longer  ;  but  it 
has  been  tried  long  enough  to  establish  this  remarkable 
fact,  that  charcoal  can  be  dissipated  by  a  heat  much  less  than 
has  been  considered  necessary  to  burn  it. 

It  may  be  supposed  that  I  was  very  desirous  of 
knowing  whether  the  same  thing  would  occur  to  charcoal 
already  formed  by  the  usual  process.  Accordingly  I 
took  a  piece  of  charcoal  from  my  kitchen,  heated  it  to  a 
strong  red  heat,  and,  while  it  was  still  red,  put  it  into  a 
marble  mortar,  and  powdered  it.  Having  passed  it 
through  a  sieve,  I  took  4.03  grammes  of  the  powder, 
placed  it  in  the  saucer,  heated  it  in  the  stove  twelve 
hours,  and  then  left  it  twelve  hours  to  cool.  On  taking 
it  out,  it  weighed  but  3.81  grammes. 

As  this  powdered  charcoal  was  nothing  but  a  collec- 
tion of  small  bits  of  charcoal,  which  were  in  contact 
with  the  air  only  by  a  very  small  surface  compared  with 
that  of  the  shavings,  I  made  another  experiment,  the  re- 
sult of  which  was  more  striking  and  more  satisfactory. 

Having  enclosed  in  a  cloth  a  quantity  of  powdered 
charcoal,  that  had  been  passed  through  a  sieve,  I  beat  it 
strongly  in  a  place  where  the  air  was  still  ;  and  when  the 
air  appeared  to  be  well  loaded  with  the  fine  dust  of  the 
charcoal,  I  placed  on  the  ground  a  white  china  saucer, 
quitted  the  place,  and  left  the  dust  to  settle. 

The  saucer  was  covered  with  it,  so  as  to  appear  of  a 
very  dark  gray. 

Before  all  the  dust  had  settled,  I  wrote  some  letters 
on  the  saucer  with  the  point  of  my  finger,  and  these  let- 
ters were  afterward  covered  with  a  still  finer  dust. 


366  Account  of  some  new  Experiments 

I  imagined  it  possible  that  the  part  covered  by  a  very 
fine  dust  might  be  found  whitened,  while  that  covered 
with  a  stratum  of  coarser  charcoal  powder  would  be 
found  perhaps  still  black. 

The  result  of  the  experiment  showed  that  this  pre- 
caution was  not  necessary.  All  the  charcoal  powder 
disappeared  completely  in  the  stove,  and  the  saucer 
came  out  perfectly  white. 

Another  saucer,  which  had  been  blackened  a  little  by 
rubbing  it  with  lampblack,  and  placed  in  the  stove  by 
the  side  of  that  blackened  with  charcoal  dust,  came  out 
of  the  stove  as  black  as  it  went  in.  As  soon  as  I  saw 
that  the  linden  shavings  converted  into  charcoal  might 
be  dissipated  by  the  moderate  heat  of  the  stove,  I  sus- 
pected that  they  had  been  consumed  slowly  by  a  silent 
and  invisible  combustion,  and  that  the  product  of  this 
combustion  could  be  nothing  but  carbonic  acid  gas. 

To  clear  up  this  point  I  made  the  following  experi- 
ment. 

Having  procured  a  stock  of  very  dry  birch  shavings 
in  ribands  about  a  twentieth  of  a  line  thick,  near  half 
an  inch  broad,  and  six  inches  long,  I  dried  them  for 
eight  days  in  a  room  heated  by  a  stove,  where  the  tem- 
perature was  about  60°  F.,  the  shavings  being  laid  on  a 
table  at  a  distance  from  the  stove.  Of  these  shavings 
thus  dried,  I  took  10  grammes,  which  I  placed  on  a 
china  plate,  and  heated  in  the  stove,  in  the  manner 
already  described,  for  twenty-four  hours.  When  taken 
out  of  the  stove,  they  weighed  but  7.7  grammes,  and 
had  acquired  a  deep  brown  colour  inclining  to  purple. 
They  were  still  wood,  however ;  for,  though  deeply 
browned,  they  burned  with  a  very  fine  flame. 

Of  these  brown  shavings  I   made  three  parcels,  each 


on  Wood  and  Charcoal.  367 

weighing  2.3  grammes.  The  first  was  placed  in  the 
stove  on  a  white  china  plate,  supported  by  a  tile,  but 
not  covered.  The  second  was  put  into  it  in  a  similar 
manner,  except  that  it  was  covered  with  a  glass  jar,  6 
inches  in  diameter  and  6  inches  high. 

The  third  parcel  was  put  into  a  glass  vessel,  6  inches 
high,  but  only  an  inch  and  a  quarter  in  diameter.  This 
narrow  vessel  was  put  into  a  glass  jar  3  inches  in  diameter 
and  7  inches  high,  which,  being  slightly  closed  with  its 
glass  cover,  was  also  placed  in  the  stove  on  a  tile. 

As  the  door  of  the  stove  (which  is  double,  the  better 
to  confine  the  heat)  does  not  shut  so  close  as  to  prevent 
the  free  passage  of  air,  and  as  the  china  plates  on 
which  two  of  the  parcels  were  placed  were  flat,  every 
circumstance  was  favourable  for  the  free  transmission  of 
the  carbonic  acid  gas  arising  from  the  decomposition  of 
these  two  parcels  by  slow  combustion,  and  there  was 
nothing  to  prevent  the  progress  of  this  operation.  But 
the  third  parcel  being  enclosed  in  a  narrow  vessel,  as 
this  gas  is  much  heavier  than  atmospheric  air,  the  first 
portion  of  this  gas  arising  from  a  commencement  of 
combustion  of  the  wood  could  not  fail  to  descend  in 
the  vessel  toward  its  bottom,  gradually  expel  the  air, 
and  at  length  fill  the  vessel  completely ;  and  as  this  sort 
of  inundation  by  carbonic  acid  gas  could  not  fail  to 
stop  the  combustion,  I  expected  to  find  that  this  parcel 
of  shavings  would  be  preserved,  at  least  in  part,  even 
though  both  the  others  should  be  entirely  consumed. 

The  stove  having  been  heated  in  the  usual  manner,  I 
found  the  next  day  that  the  results  of  the  experiment 
had  been  such  as  I  anticipated.  The  two  parcels  of 
shavings  placed  on  the  china  plates  had  disappeared  en- 
tirely, nothing  at  all  remaining  except  a  very  small 


368  Account  of  some  new  Experiments 

quantity  of  ashes,  of  a  white  colour  inclining  a  little  to 
yellow. 

The  yellow  ashes  in  the  plate  that  was  not  covered 
with  a  glass  jar  were  deranged  and  dispersed  by  the 
wind  occasioned  by  opening  the  door  of  the  stove  too 
suddenly ;  but  those  in  the  other  plate,  being  protected 
by  the  glass,  were  found  all  together.  As  they  still  re- 
tained their  original  figure  of  shavings,  though  reduced 
to  a  very  small  bulk,  this  appeared  to  me  a  demonstra- 
tive proof  that  the  shavings,  whence  they  arose,  had  not 
been  burned  by  a  common  fire.  For  this  reason,  and 
also  on  account  of  their  extraordinary  colour,  approach- 
ing very  near  that  of  the  wood  in  its  natural  state,  I 
preserved  them,  to  show  them  to  the  Class.  They 
weighed  only  0.04  of  a  gramme  ;  and  as  the  shavings, 
of  which  they  were  the  remains,  weighed  2.987  grammes 
on  coming  out  of  the  hands  of  the  joiner,  these  ashes 
make  only  one  and  one  third  per  cent  of  the  weight 
of  the  wood. 

The  third  parcel  of  shavings,  which  had  been  placed 
in  a  narrow  glass  vessel,  had  not  disappeared,  but  the 
wood  was  converted  into  perfect  charcoal.  I  have  the 
honour  to  present  it  to  the  Class,  in  the  same  vessel  in 
which  it  was  charred. 

As  the  three  parcels  of  shavings  were  of  the  same 
wood,  and  equal  in  weight ;  as  they  were  exposed  to- 
gether to  the  same  degree  of  heat,  and  for  the  same 
time ;  and  as  the  two  portions  that  were  placed  so  as  to 
facilitate  the  escape  of  the  carbonic  acid  gas  arising  from 
their  decomposition,  disappeared  entirely,  while  the 
third,  which  was  so  circumstanced  that  the  escape  of  this 
gas  was  impossible,  did  not  disappear  ;  —  it  seems  to  me 
that  there  can  be  no  doubt  of  the  cause  of  the  phenom- 


on  Wood  and  Charcoal.  369 

ena  that  presented  themselves  ;  and  it  is  certainly  a 
curious  fact,  that  charcoal,  which  has  hitherto  been  con- 
sidered as  one  of  the  most  fixed  substances  known,  can 
unite  itself  to  oxygen,  and  form  with  it  carbonic  acid 
gas,  at  a  temperature  much  below  that  at  which  it  burns 
visibly. 

[This  paper  is  printed  from  Nicholson's  Journal,  XXXII.  (1812), 
pp.  100—  105.] 


RESEARCHES 


HEAT    DEVELOPED    IN    COMBUSTION  AND    IN    THE 
CONDENSATION   OF   VAPOURS. 

SECTION  I.  —  Description  of  a  new  Calorimeter. 

\  TTEMPTS  have  been  long  ago  made  to  measure 
JT\.  the  heat  that  is  developed  in  the  combustion  of 
inflammable  substances ;  but  the  results  of  the  experi- 
ments have  been  so  contradictory,  and  the  methods 
employed  so  little  calculated  to  inspire  confidence,  that 
the  undertaking  is  justly  considered  as  very  little  ad- 
vanced. 

I  had  attempted  it  at  three  different  times  within 
these  twenty  years,  but  without  success.  After  having 
made  a  great  number  of  experiments  with  the  most 
scrupulous  care,  with  apparatus  on  which  I  had  long 
reflected,  and  afterward  caused  to  be  executed  by  skilful 
workmen,  I  had  found  nothing,  however,  that  appeared 
to  me  sufficiently  decisive  to  deserve  to  be  made  public. 
A  large  apparatus  in  copper  more  than  twelve  feet  long, 
which  I  had  made  at  Munich  fifteen  years  ago,  and 
another,  scarcely  less  expensive,  made  at  Paris  four  years 
ago,  which  I  have  still  in  my  laboratory,  attest  the  de- 
sire I  have  long  entertained  of  finding  the  means  of 
elucidating  a  question^  that  has  always  appeared  to  me 
of  great  importance,  both  with  regard  to  the  sciences 
and  to  the  arts. 


On  the  Heat  developed  in  Combustion,  etc.      371 

At  length,  however,  I  have  the  satisfaction  of  an- 
nouncing to  the  Class,  that,  after  all  my  fruitless 
attempts,  I  have  discovered  a  very  simple  method  of 
measuring  the  heat  manifested  in  combustion,  and  this 
even  with  such  precision  as  leaves  nothing  to  be  desired. 

That  the  Class  may  be  the  better  able  to  judge  of  my 
method  of  operating,  and  the  reliance  that  may  be 
placed  on  the  results  of  my  experiments,  I  place  my 
apparatus  before  it. 

The  principal  part  of  this  apparatus  is  a  kind  of 
prismatic  receiver,  eight  inches  long,  four  inches  and  a 
half  broad,  and  four  inches  three  quarters  high,*  formed 
of  very  thin  sheets  of  copper.  This  receiver,  which  well 
deserves  the  name,  already  celebrated,  of  calorimeter ',  is 
furnished  with  a  long  neck,  near  one  of  its  extremities, 
three  quarters  of  an  inch  in  diameter,  and  three  inches 
high,  intended  to  receive  and  support  a  mercurial  ther- 
mometer of  a  particular  shape.  The  receiver  has  also 
another  neck,  an  inch  in  diameter  and  the  same  in 
height,  situate  in  the  centre  of  its  upper  part,  and  closed 
by  a  cork. 

Within  this  receiver,  two  lines  above  its  flat  bottom, 
is  a  particular  kind  of  worm,  receiving  all  the  products 
of  the  combustion  of  the  inflammable  substances  burned 
in  the  experiments,  and  transmitting  the  heat  manifested 
in  this  combustion  to  a  considerable  body  of  water, 
which  is  in  the  receiver. 

This  worm,  which  is  made  of  thin  copper,  occupies 
and  covers  the  whole  bottom  of  the  receiver,  yet  with- 
out touching  either  its  bottom  or  its  sides.  It  is  a  flat 
tube,  an  inch  and  a  half  broad  at  one  end  and  an  inch  at 
the  other,  and  half  an  inch  thick  throughout.  It  is 

*  French  measure. 


372  On  the  Heat  developed  in  Combustion 

bent  horizontally,  so  as  to  pass  three  times  from  one 
end  of  the  receiver  to  the  other,  and  is  supported  in  its 
place,  two  lines  above  the  bottom  of  the  receiver,  by 
several  little  feet. 

The  aperture  that  forms  the  mouth  of  the  worm  is 
a  circular  hole  in  its  bottom,  near  its  broadest  end. 
Into  this  hole  is  soldered  a  perpendicular  tube,  an  inch 
in  length  and  an  inch  in  diameter,  reaching  within  the 
worm  to  the  height  of  a  quarter  of  an  inch  above  its 
bottom. 

This  tube  passes  through  a  circular  hole  in  the  bot- 
tom of  the  receiver,  to  which  also  it  is  soldered.  Its 
lower  aperture  is  seven  lines  below  the  bottom  of  the 
receiver ;  and  through  this  the  products  of  the  combus- 
tion enter  into  the  worm. 

The  other  extremity  of  the  worm  passes  horizontally 
through  the  perpendicular  end  of  the  receiver,  opposite 
to  that  near  which  the  products  of  the  combustion  enter 
the  worm. 

The  worm,  before  it  passes  through  the  end  of  the 
receiver,  is  fashioned  into  the  shape  of  a  round  pipe, 
half  an  inch  in  diameter ;  and  an  inch  in  length  of  this 
pipe  is  seen  without  the  receiver.  This  piece  is  made 
to  fit  tight  into  another  similar  tube,  belonging  to  the 
worm  of  another  receiver,  which  I  call  the  secondary 
receiver ;  the  purpose  of  which  is  to  receive  the  heat 
that  might  still  be  found  in  the  products  of  combustion, 
after  they  have  passed  through  the  worm  of  the  prin- 
cipal receiver. 

To  support  these  two  receivers  in  the  air,  so  as  not 
to  touch  the  table  that  supports  them,  each  of  them  is 
fixed  in  a  frame  of  dry  linden  wood,  made  of  rods  an 
inch  square.  Round  the  bottom  of  each  receiver  is  a 


and  in  the  Condensation  of  Vapours.          373 

copper  rim,  three  lines  deep,  which  is  fastened  by  a  row 
of  very  small  nails  to  the  wooden  frame.  The  body  of 
the  receiver  itself  enters  about  a  line  into  the  frame,  to 
which  it  is  very  accurately  fitted. 

The  flat  form  of  the  worm  is  essential  to  the  perfec- 
tion of  the  apparatus,  as  is  evident  when  its  purpose  is 
considered. 

All  the  products  of  the  combustion  being  elastic 
fluids,  and  consequently  substances  incapable  of  com- 
municating their  heat  but  by  proceeding  particle  after 
particle  to  deposit  it  on  the  surface  of  the  cold  and 
fixed  body  intended  to  receive  it,  it  was  indispensable  so 
to  construct  the  apparatus  that  the  hot  fluids  should  of 
necessity  be  spread  beneath  and  against  a  large  flat  sur- 
face, placed  horizontally,  and  always  cold. 

Before  I  employed  horizontal  worms  made  of  flat 
tubes,  I  had  more  than  once  tried  those  of  the  common 
form  ;  but  they  never  answered  my  purpose  otherwise 
than  so  imperfectly  that  I  could  never  make  any  account 
of  the  experiments  in  which  they  were  employed. 
There  is  no  doubt  but  the  shape  I  have  adopted  for  the 
worm  of  my  calorimeter  would  be  very  advantageous 
for  every  kind  of  apparatus  for  distillation. 

One  thing  very  important  in  the  construction  of  my 
apparatus  is  the  shape  of  the  thermometer  which  I 
employ  to  measure  the  temperature  of  the  water  in  the 
receiver.  This  thermometer  —  which  I  made  myself,  and 
which,  after  having  undergone  every  kind  of  trial,  has 
always  appeared  good  —  is  a  mercurial  thermometer, 
divided  according  to  Fahrenheit's  scale.  It  is  one  of 
four,  all  similar,  that  I  employed  at  Munich,  in  the 
winter  of  1802,  in  my  experiments  on  the  refrigeration 
of  liquids  enclosed  in  vessels. 


374          On  Mie  Heat  developed  in  Combustion 

The  reservoir  of  this  thermometer  is  cylindrical, 
about  two  lines  in  diameter  only,  and  four  inches  high ; 
and  as  the  water  in  my  calorimeter  is  four  inches  deep, 
this  thermometer  always  indicates  the  mean  temperature 
of  the  fluid,  whatever  may  be  the  temperature  of  its 
different  strata. 

In  my  various  inquiries  concerning  heat,  I  have  had 
frequent  opportunities  of  seeing  the  importance  of  this 
precaution  ;  and  I  cannot  conceive  how  any  one  can 
expect  to  avoid  great  mistakes  in  measuring  the  temper- 
ature of  liquids  heated  or  cooled,  if  we  do  not  attend 
to  this.  For  my  own  part,  I  confess  I  pay  little  regard 
to  the  experiments  of  which  I  am  told,  when  I  know 
they  are  so  negligently  made  ;  and  assuredly  I  shall 
never  waste  my  time  in  attempting  to  build  theories  on 
their  results. 

In  using  the  apparatus  I  have  described,  several  pre- 
cautions are  necessary.  In  the  first  place,  it  is  obvious 
that  when  the  object  is  to  ascertain  the  quantity  of  heat 
developed  in  the  combustion  of  any  inflammable  sub- 
stance, it  is  indispensably  necessary  so  to  arrange  mat- 
ters that  the  combustion  shall  be  complete.  I  have  thought 
that  it  might  be  so  considered,  whenever  the  substance 
burned  leaves  no  residuum,  and  burns  with  a  clear 
flame,  without  smoke  or  smell. 

The  least  smell,  particularly  that  peculiar  to  the  in- 
flammable substance  burned,  is  a  certain  indication  that 
the  combustion  is  imperfect. 

I  had  long  sought,  before  I  was  able  to  find,  to  my 
satisfaction,  a  mode  of  burning  very  volatile  liquids, 
such  as  alcohol  and  ether  ;  but  I  have  at  length  discov- 
ered it,  as  will  soon  appear.  I  have  frequently  suc- 
ceeded in  burning  highly  rectified  sulphuric  ether,  with- 


and  in  the  Condensation  of  Vapours.  375 

out  the  least  smell  of  ether  being  diffused  through  the 
room  ;  and  it  was  in  these  instances  alone  that  I  con- 
sidered the  experiments  as  accurate. 

As  to  wood,  I  have  found  a  very  simple  method  of 
burning  it  completely,  without  the  least  appearance  of 
smoke  or  smell.  I  got  a  joiner  to  plane  me  shavings 
about  half  an  inch  wide,  a  tenth  of  a  line  thick,  and  six 
inches  long;  and  holding  these  in  the  hand  or  with 
pliers,  elevated  at  an  angle  of  45°  or  thereabout,  and 
with  the  edges  perpendicular,  they  burned  like  a  match, 
with  a  very  clear  flame. 

The  slip  of  wood  that  burns  being  very  thin,  and  placed 
between  two  flat  flames  which  press  on  it  closely,  it  is 
exposed  to  the  action  of  so  strong  a  heat  that  it  burns 
perfectly  and  entirely. 

If  the  shavings  employed  be  too  thick,  a  portion  of 
the  charcoal  of  the  wood  remains,  particularly  if  it  be 
oak,  or  any  other  wood  of  slow  and  difficult  combus- 
tion ;  and  in  this  case  the  experiments  are  defective. 
But  if  the  shavings  be  sufficiently  thin>  and  well  dried, 
I  have  found  that  any  kind  of  wood  may  be  burned 
completely. 

In  burning  candles,  wax  tapers,  or  fat  oils  in  lamps, 
the  only  precautions  necessary  are  so  to  arrange  the 
wick  as  to  yield  no  smoke  ;  to  place  the  flame  properly 
in  the  aperture  of  the  worm ;  and  to  surround  the 
apparatus  on  all  sides  by  screens,  to  prevent  the  flame 
from  being  deranged  by  the  wind. 

In  these  experiments  there  is  one  source  of  error, 
too  obvious  to  escape  the  most  superficial  observer,  and 
to  which  it  was  important  to  attend.  While  the  calo- 
rimeter is  warmed  by  the  heat  developed  in  the  combus- 
tion of  the  inflammable  substance  which  is  burning  at 


376  On  the  Heat  developed  in  Combustion 

the  aperture  of  the  worm,  it  is  continually  cooled  by 
the  ambient  air  that  surrounds  it  on  all  sides.  It  would 
be  possible,  no  doubt,  by  calculations  founded  on  a 
knowledge  of  the  law  of  refrigeration  of  the  receiver, 
which  might  be  found  by  separate  experiments,  to  ascer- 
tain the  quantity  of  the  effect  produced  by  the  refrigera- 
tion in  question  ;  and  this  even  with  a  certain  degree  of 
precision  :  but  it  would  have  been  impossible  by  this 
method,  or  by  any  other  known,  to  calculate  the  effects 
of  another  cause  of  error,  less  obvious  perhaps,  but 
certainly  more  weighty,  than  that  of  the  refrigeration 
of  the  external  surface  of  the  receiver. 

The  nitrogen  which  is  mixed  with  the  oxygen  of  the 
atmospheric  air  is  necessarily  carried  into  the  worm 
with  the  proper  products  of  the  combustion  ;  and  with- 
out a  precaution,  which  it  occurred  to  me  to  employ  to 
prevent  the  effects  of  this  cause  of  error  by  making 
a  compensation  for  them,  all  the  experiments  would 
have  been  of  no  value. 

Fortunately  the  method  I  employed  to  obviate  the 
effects  of  this  cause  of  error  was  sufficient  to  prevent  at 
the  same  time  those  that  might  have  arisen  from  the 
cooling  of  the  outer  surface  of  the  receiver. 

As  the  receiver  is  cooled,  whether  by  the  atmospheric 
air  in  contact  with  its  external  surface  or  by  the  nitro- 
gen and  other  gases  traversing  the  worm  with  the 
products  of  combustion,  only  so  far  as  the  worm  is 
hotter  than  the  surrounding  air,  while,  on  the  contrary, 
it  is  heated  by  these  elastic  fluids  whenever  it  is  at  a 
lower  temperature  than  they  are,  — by  arranging  matters 
so  that  the  temperature  of  the  water  in  the  receiver  shall 
be  a  certain  number  of  degrees,  5°  for  instance,  below 
the  temperature  of  the  air  at  the  beginning  of  the  ex- 


and  in  the  Condensation  of  Vapours.  377 

periment,  and  putting  an  end  to  the  experiment  as  soon 
as  the  water  in  the  receiver  has  acquired  a  temperature 
precisely  the  same  number  of  degrees  higher  than  the 
air,  the  receiver  will  be  heated  by  the  air  during  half 
the  time  of  continuance  of  the  experiment,  and  cooled 
by  it  during  the  other  half;  so  that  the  calorific  and  fri- 
gorific  effects  of  the  air  on  the  apparatus  will  counter- 
balance each  other,  and  produce  no  perceptible  effect  on 
the  results  of  the  experiments  ;  consequently  they  will 
require  no  correction. 

When  we  are  making  experiments  to  elucidate  natural 
phenomena,  it  is  always  more  satisfactory  to  avoid 
errors,  or  to  compensate  them,  than  to  trust  to  calcu- 
lation for  appreciating  their  effects. 

As  the  law  of  the  variation  of  the  specific  heat  of  water 
at  different  temperatures  is  not  known,  and  as  we  have 
but  an  imperfect  knowledge  of  the  true  measure  of  the 
intervals  of  temperature  marked  by  the  divisions  of  our 
thermometers,  to  prevent  the  effects  that  our  uncertainty 
on  these  points  would  have  on  the  subject  of  inquiry,  I 
took  care  to  make  my  experiments  in  a  room  where  the 
temperature  varied  very  little,  and  to  confine  them  to  a 
few  degrees  of  elevation  of  the  temperature  of  the  water 
in  the  receiver. 

It  is  true,  I  made  some  experiments  in  a  room  where 
the  air  was  much  colder,  and  in  which  I  employed  ice 
instead  of  water  to  fill  the  receiver ;  but  these  experi- 
ments were  for  a  particular  purpose,  and  are  not  classed 
with  the  others.  Besides,  they  never  afforded  such 
uniform  and  satisfactory  results  as  those  made  under 
other  circumstances. 

It  has  been  fully  proved,  not  only  by  the  results  of 
my  experiments,  but  by  the  experiments  of  others  also, 


37 8  On  the  Heat  developed  in  Combustion 

that  the  vapour  of  water  in  contact  with  ice  frequently 
freezes,  while  this  same  ice  is  melting  by  the  heat,  or 
that  its  thaw  appears  fully  established. 

To  give  an  idea  of  the  reliance  that  may  be  placed  on 
the  results  of  the  experiments  made  with  the  new  appa- 
ratus I  have  just  described,  I  will  introduce  here  the 
particulars  of  an  experiment  made  purposely  to  discover 
its  degree  of  perfection. 

Having  filled  two  receivers,  properly  connected  with 
each  other,  with  water  at  the  temperature  of  the  air  of 
the  room,  55°  F.,  I  burned  a  wax  taper  under  the  mouth 
of  the  principal  receiver,  so  that  all  the  products  of  the 
combustion  passed  through  the  worm  of  the  secondary 
receiver,  after  having  traversed  that  of  the  principal. 
Each  of  the  receivers  contained  2371  grammes  [36621.5 
grains]  of  water. 

The  following  are  the  results  of  the  experiment :  — 


TIME   OF   THE   OBSERVATION. 

Hour,        Mia.          Sea 


9         37  55° 

49  42  65 

56  15  70 

10  2  52  75 

9  32  80 

16  34  85 

23  54  90 

27 

31  40  95 

39  35  100 

47  4°  I05 

From  the  results  of  this  experiment  it  appears  that 
the  water  in  the  secondary  receiver  did  not  begin  to  be 
heated  perceptibly  till  that  in  the  principal  receiver  had 
been  heated  15°  or  20°;  and,  as  I  had  intended  from 
the  beginning  never  to  continue  an  experiment  longer 
than  was  necessary  to  raise  the  temperature  of  the 


and  in  the  Condensation  of  Vapours.  379 

water  in  the  principal  receiver  10°  or  12°  F.,  it  may  be 
supposed  that,  as  soon  as  I  found  by  this  experiment 
how  little  heat  remained  in  the  products  of  combustion 
after  they  had  passed  through  the  worm  of  the  principal 
receiver,  I  relinquished  my  original  design  of  operating 
with  the  two  receivers  joined  together.  As  it  was  evi- 
dent, from  the  above  results,  that  the  second  receiver 
could  never  be  sensibly  affected,  or  indicate  anything 
except  the  confidence  I  might  place  in  the  indications 
of  the  first,  I  resolved  to  dispense  with  the  trouble  of 
using  it. 

It  may  be  seen  by  the  description  I  have  given  of 
this  apparatus,  that  it  may  be  used  very  conveniently 
for  ascertaining  the  specific  heat  of  gases,  as  well  as 
that  made  apparent  in  the  condensation  of  vapours,  and 
generally  in  all  researches  where  the  quantity  of  heat 
communicated  by  an  elastic  fluid  in  cooling  is  to  be 
measured.  And  as  it  would  be  extremely  easy,  by  very 
simple  means,  to  separate  completely  the  products  of 
the  vapours  condensed  in  the  worm  from  the*  gases 
that  pass  through  it  without  being  condensed,  I  cannot 
avoid  hoping  that  this  apparatus  will  become  useful  as 
an  instrument  to  be  employed  in  chemical  analyses. 
This,  however,  would  only  be  an  extension  of  the 
method  already  employed  with  so  much  success  by 
M.  de  Saussure,  and  by  Messrs.  Gay  Lussac  and 
Thenard. 

As  soon  as  my  apparatus  was  finished,  I  was  eager 
to  see  what  quantity  of  heat  I  should  find  in  the  com- 
bustion of  wax  and  in  that  of  olive  oil,  that  I  might 
afterward  compare  the  results  of  my  experiments  with 
those  of  M.  Lavoisier's ;  and,  as  I  have  the  most 
implicit  reliance  on  everything  published  by  that  excel- 


380          On  the  Heat  developed  in  Combustion 

lent  man,  I  sincerely  wished  to  find  in  this  comparison 
a  proof  of  the  accuracy  of  my  method,  and  at  the  same 
time  a  confirmation  of  the  estimates  of  M.  Lavoisier. 


SECTION  II.  —  Experiments  made  with  white  Wax. 

The  air  of  the  room  being  at  the  temperature  of  6 1°  F., 
2781  grammes  of  water,  of  the  temperature  of  56°  F., 
were  put  into  the  receiver  of  the  calorimeter  (including 
the  quantity  of  this  liquor  that  represents  the  specific 
heat  of  the  instrument),  and,  a  lighted  wax  taper  having 
been  properly  placed  at  the  entrance  of  the  worm,  the  calo- 
rimeter was  heated  for  13  minutes  and  26  seconds,  when, 
the  thermometer  announcing  that  the  water  had  acquired 
the  temperature  of  66°  F.,  the  taper  was  extinguished. 

As  I  took  care  to  weigh  the  taper  before  it  was  lighted, 
I  found,  by  weighing  it  at  the  end  of  the  experiment, 
that  1.63  grammes  of  wax  had  been  burned. 

To  express  the  results  of  this  experiment  so  as  to  ren- 
der them  obvious,  and  at  the  same  time  easy  to  be  com- 
pared with  the  results  of  other  similar  experiments,  we 
will  see  how  much  water  of  the  temperature  of  melting 
ice  would  have  been  made  to  boil,  at  the  mean  pressure 
of  the  atmosphere,  by  the  heat  made  apparent  in  the 
combustion  of  the  1.63  grammes  of  wax  burned. 

The  distance  on  Fahrenheit's  scale  between  the  tem- 
perature of  melting  ice  and  boiling  water  being  180°,  if 
the  burning  of  1.63  grammes  of  wax  were  requisite  to 
raise  the  temperature  of  the  water  in  the  calorimeter  10°, 
the  burning  of  29.34  grammes  would  have  been  necessary 
to  raise  it  180°;  and,  if  29.34  grammes  of  wax  could 
furnish  by  combustion  sufficient  heat  to  raise  the  tem- 
perature of  2781  grammes  180°,  a  gramme  of  this 


and  in  the  Condensation  of  Vapours.  38 1 

inflammable  substance  must  furnish  enough  to  heat 
94.785  grammes  of  water  to  the  same  point. 

Consequently,  one  pound  of  white  wax,  or  wax  taper, 
should  furnish,  in  burning,  sufficient  heat  to  raise  94.785 
pounds  of  water  from  the  temperature  of  melting  ice  to 
the  boiling  point. 

To  find  how  many  pounds  of  ice  this  quantity  of  heat 
would  melt,  we  have  only  to  add  to  the  number  of  pounds 
of  water  at  the  temperature  of  melting  ice  it  would  cause 
to  boil  the  third  part  of  this  number,  and  the  sum  would 
express  the  weight  of  the  ice  in  pounds. 

This,  then,  for  white  wax  is  :  — 

94-78$ 
+  31-595 


=  1 26.380  IBs.  of  ice  melted  for  I  Ib.  of  the  wax  burned. 

Before  I  compare  the  result  of  this  experiment  with 
that  of  an  experiment  made  with  the  same  substance  by 
M.  Lavoisier,  I  will  give  an  account  of  two  other  ex- 
periments I  made  with  wax,  as  the  reader  will  undoubt- 
edly be  struck  with  the  uniformity  of  their  results.  This 
is  so  remarkable  that  I  should  scarcely  venture  to  pub- 
lish them  had  I  not  proofs  that  all  my  experiments  were 
actually  made  and  minuted  down  before  I  began  my  cal- 
culation of  their  results,  and  were  I  not  assured  that 
any  person  who  will  follow  my  method,  using  the  same 
apparatus,  will  find  the  same  results  on  repeating  my 
experiments. 

As  the  mode  of  operating  in  making  these  experiments 
must  now  be  well  known,  I  may  suppress  the  particulars 
in  what  follows  without  inconvenience,  and  give  only  the 
results  of  the  experiments. 

I  will  begin  with  three  experiments  made  with  white 


382  On  the  Heal  developed  in  Combustion 


wax;  and  to  render  them  more  easy  to  compare,  I  will 
give  them  together  in  a  tabular  form. 

Results  of  three  Experiments  on  the  Burning  of  white  Wax,  showing  the 
Quantity  of  Water  that  would  be  heated  1 80°,  or  of  Ice  that  would 
he  melted,  by  one  pound  Weight  of  it. 


1 

Temp,  of  the  water 

Results. 

u  Quantity 
•5  of  wax 
^  butned. 

£ 

employed 
ing. 

Quantity 
of  water 
heated. 

of  its 
tempera- 
ture. 

at  the  be- 
ginning of 
the  exp. 

at  the 
end  of  the 
exp. 

Tempera- 
ture of 
the  air. 

Pounds 
of  water 
heated 

1  80° 

Pounds 
of  ice 

melted. 

Grms. 
1  1.63 
2  2.36 

m.      s. 
13    24 
I9    30 

Grms. 
2781 

Degrees. 

io°F. 
Hi 

Degrees. 
51 

Degrees. 
65*    ' 

Degrees. 

61°  F. 

58 

Ibs. 
94.785 
94.926 

Ibs. 
126.38 
126.608 

3  2.17 

18  15 

<3i 

5»i 

6 

58 

94-337J125.783 

If  we  take  the  mean  term  between  the  results  of  these 
experiments,  we  shall  find  that  the  quantity  of  heat  de- 
veloped in  the  combustion  of  wax  is  such  that  one  pound 
of  this  substance  is  sufficient  to  raise  94.682  pounds  of 
water  from  the  temperature  of  melting  ice  to  the  boiling 
point,  and  consequently  that  it  should  melt  126.242 
pounds  of  ice. 

According  to  the  experiments  of  M.  Lavoisier,  the 
heat  developed  in  the  combustion  of  one  pound  of  white 
wax  was  sufficient  to  melt  133.166  pounds  of  ice. 

The  difference  between  the  results  of  our  experiments 
with  this  substance  is  not  very  great ;  and  if  those  of 
M.  Lavoisier  were  made  at  a  time  when  the  temperature 
of  the  air  was  only  a  few  degrees  higher  than  that  of 
melting  ice  (which  I  have  no  means  of  ascertaining),  the 
quantity  of  nitrogen  that  must  have  entered  into  the 
calorimeter,  with  the  oxygen  employed  to  support  the 
combustion,  would  have  been  so  great  as  to  account  suf- 
ficiently for  the  difference.  But  the  very  great  difference 


and  in  the  Condensation  of  Vapours.  383 

between  the  results  of  our  experiments  made  with  olive 
oil  proves  that  one  or  other  of  our  processes  must  have 
been  defective. 

The  mean  result  of  several  experiments  made  with 
olive  oil  gave  me  for  the  measure  of  the  quantity  of  heat 
developed  in  the  combustion  of  one  pound  of  this  sub- 
stance 90.439  pounds  of  water  heated  180°  F.,  or  120 
pounds  of  ice  melted,  neglecting  the  fraction. 

In  the  experiments  of  M.  Lavoisier,  more  than  148 
pounds  of  ice  were  melted  by  the  heat  that  appeared  to 
result  from  the  combustion  of  one  pound  of  this  oil. 

It  is  true  that  this  result  was  considered  by  that  emi- 
nent philosopher  himself  as  too  great  to  be  capable  of 
explanation ;  and  he  added,  with  that  modesty  which 
rendered  him  so  engaging  and  so  respectable:  "We 
shall  probably  find  ourselves  under  the  necessity  of 
making  corrections,  perhaps  pretty  considerable  ones, 
in  most  of  the  results  I  have  given  ;  but  I  did  not 
think  this  a  sufficient  reason  to  delay  affording  their 
assistance  to  those  who  might  intend  to  pursue  the 
same  object." 

As  it  appears  very  probable  that  all  the  fat  oils,  when 
perfectly  pure,  are  composed  of  the  same  principles,  I 
was  curious  to  see  whether  rape  oil,  purified  by  sulphuric 
acid,  would  not  afford  more  heat  in  its  combustion  than 
olive  oil,  when  burned  in  its  natural  state.  The  result 
of  three  experiments  showed  me  that  rape  oil,  thus  puri- 
fied, does,  in  fact,  yield  more  heat  than  olive  oil.  The 
difference  is,  indeed,  pretty  considerable,  and  more  than 
I  could  have  suspected. 

The  combustion  of  I  Ib.  of  purified 

rape  oil  gave        .          .         .         93.073  Ibs.  of  water  heated  1 80°. 
I  Ib.  of  olive  oil  gave  .         .     90.439  "          "         "         " 


384  On  the  Heat  developed  in  Combustion 

Chemists  may  tell  us  whether  the  quantity  of  incom- 
bustible matter  separated  from  rape  oil  in  purifying  it 
be  sufficient,  or  not,  to  account  for  this  difference. 

On  comparing  the  results  of  the  experiments  made 
with  white  wax  and  those  with  the  purified  oil,  it 
appears  that  equal  weights  of  these  substances  afford 
nearly  equal  quantities  of  heat  in  their  combustion;  and 
as,  in  fact,  this  ought  to  be  the  case,  from  the  quantities 
of  combustible  matter  they  contain,  the  result  tends  to 
strengthen  our  confidence  in  this  method  of  measuring 
the  heat  developed  in  combustion. 

The  combustion  of 

I  Ib.  of  white  wax  gave  .          94.682  Ibs.  of  water  heated  1 80°. 
I  Ib.  of  purified  oil     .         .     93.073    "  "         "  " 

As  the  object  I  had  chiefly  in  view  in  this  series  of 
experiments  was  to  ascertain  the  quantities  of  heat 
developed  in  the  combustion  of  pure  hydrogen  and 
carbon,  in  order  to  render  this  method  useful  in  some 
chemical  analyses,  I  examined  particularly  those  in- 
flammable substances  that  had  been  analyzed  with  most 
care. 

Several  attempts  have  been  made  to  ascertain  these  in- 
teresting questions  by  direct  experiments,  in  burning 
pure  hydrogen,  or  pure  hydrogen  and  carbon ;  but  the 
results  of  these  researches  have  varied  so  much  that  they 
cannot  be  relied  on. 

According  to  Crawford,  the  heat  developed  in  the 
combustion  of  one  pound  of  hydrogen  gas  is  sufficient 
to  raise  the  temperature  of  410  pounds  of  water  180°  F. 
But  the  estimation  of  M.  Lavoisier  is  much  lower. 
According  to  him,  this  heat  would  raise  only  221.69 
pounds  of  water  the  same  number  of  degrees. 


and  in  the  Condensation  of  Vapours.  385 

On  the  other  hand,  M.  Lavoisier  estimates  the  quan- 
tity of  heat  developed  in  the  combustion  of  charcoal 
much  higher  than  Dr.  Crawford.  I  have  many  reasons 
to  believe  that  they  both  estimate  it  too  high ;  and,  if 
this  opinion  be  confirmed,  we  must  estimate  the  heat  de- 
veloped in  the  combustion  of  hydrogen  a  little  higher 
even  than  Crawford  has  done,  to  be  able  to  account  for 
that  manifested  in  my  experiments. 

From  several  experiments,  which  I  made  five  years  ago, 
it  appeared  to  me  that  one  pound  of  charcoal,  dried  as 
much  as  possible  before  it  was  weighed  by  heating  it  red- 
hot  in  a  crucible,  was  not  capable  of  raising  more  than 
from  52  to  54  pounds  of  water  from  the  temperature 
of  melting  ice  to  a  boiling  heat. 

According  to  Crawford,  this  heat  should  suffice  to  boil 
57. 606  pounds,  and  according  to  Lavoisier,y2. 375  pounds. 

We  shall  see  how  these  estimates  agree  with  the  results 
of  my  experiments. 

As  the  experiments  made  with  wax  yielded  very  uni- 
form results,  and  as  the  analysis  of  this  substance  has 
been  made  with  great  care,  I  shall  examine  how  the 
quantities  of  hydrogen  and  carbon  in  this  substance 
agree  with  the  quantity  of  heat  that  it  afforded  me  in 
combustion. 

According  to  the  analysis  of  Messrs.  Gay-Lussac  and 
Thenard,  a  pound  of  this  substance  contains 

Carbon  .          .          .         .          .         ,         .          .          .     0.8179  Ib. 
Free  hydrogen    0.1191 

If  we  adopt  the  calculations  of  Dr.  Crawford,  both  for 
the  heat  furnished  by  the  hydrogen  and  that  furnished  by 
the  carbon,  we  shall  have  for  the  heat  that  should  be 
furnished  by  the  combustion 

VOL.    II.  25 


386  On  the  Heat  developed  in  Combustion 

Pounds  of  water  raised 
from  32°  to  212°. 

Of  0.1191  lb.  of  hydrogen,  after  tne  ratio  of  410 
Ibs.  of  water  raised  from  32°  to  212°  by  burning 
I  lb.  of  hydrogen 48.831  Ibs. 

Of  0.8179  lb.  of  carbon,  after  the  ratio  of  57.606 
Ibs.  of  water  raised  from  32°  to  212°  by  burning 
I  lb.  of  carbon  ......  47.116  " 


Total  of  the  heat  that  ought  to  be  furnished  by  the 
quantity  of  combustible  matter  (hydrogen  and  car- 
bon) in  i  lb.  of  white  wax  ....  95-947  " 

Quantity  of  heat  furnished  by  I  lb.  of  white  wax, 
during  its  combustion,  according  to  my  experi- 
ments   94.682  ' 

If  we  adopt  the  calculations  of  M.  Lavoisier  for  the 
heat  furnished  by  carbon  and  hydrogen  in  their  combus- 
tion, we  shall  have  for  the  heat  that  ought  to  be  furnished 
by  the  burning 

Of  0.8179  lb.  of  carbon,  after  the  ratio  of  72.375  Ibs. 

of  water  heated  1 80°  by  I  lb.          .          .          .          59. 195  Ibs. 
Of  0.1191  lb.  of  hydrogen,  after  the  ratio  of  221.69 

Ibs.  of  water  heated  180°  by  i  lb.  .         .     26.403     " 

Total  of  the  heat  that  ought  to  be  furnished  by  the 

combustible  matter  in  i  lb.  of  white  wax         .          85.598     " 

From  the  results  of  these  calculations  it  appears  that 
the  estimations  of  Dr.  Crawford  agree  much  better  with 
the  experiments  than  those  of  M.  Lavoisier. 

Let  us  see  how  the  results  of  the  experiments  made 
with  fat  oils  agree  with  the  estimations  of  these  gentle- 
men. 

According  to  the  analysis  of  Messrs.  Gay-Lussac  and 
Thenard,  a  pound  of  olive  oil  contains 

Carbon 0.7721  lb. 

Free  hydrogen         .......     0.1208 


and  in  the  Condensation  of  Vapours.  387 

According  to  the  calculations  of  M.  Lavoisier, we  have, 

For  0.7721  Ib.  of  carbon    .          55.881  Ibs.  of  water  heated  180°. 
"    0.1208  Ib.  of  hydrogen    .     26.780    "  "         "         " 

Total        ...         .         82.661    "  " 

According  to  the  calculations  of  Dr.  Crawford,  it  is, 

For  0.7721  Ib.  of  carbon    .          44-478  Ibs.  of  water  heated  180°. 
"    0.1208  Ib.  of  hydrogen   .     49-528    "  "         "         " 

Total        ....         94.006    "  "         "         " 

According  to  the  experiments,  I  pound  of  purified  rape 
oil  furnished  heat  sufficient  to  raise  93.073  pounds  of 
water  180°;  and  i  pound  of  olive  oil  enough  to  heat 
90.439  pounds. 

From  all  these  comparisons  it  follows  that  the  estima- 
tions of  Dr.  Crawford  agree  much  better  than  those  of 
M.  Lavoisier  with  the  results  of  my  experiments. 

SECTION    III.  —  Experiments   made   with  Spirit  of  Wine, 
Alcohol,  and  Sulphuric  Ether. 

As  the  component  parts  of  these  inflammable  liquids 
may  be  considered  as  well  ascertained  by  the  results  of 
the  excellent  investigation  of  M.  de  Saussure,  I  under- 
took to  examine  them  for  the  second  time,  in  order  to 
discover  what  quantities  of  heat  are  developed  in  their 
combustion.  I  had  begun  this  undertaking  five  years 
ago  ;  but,  after  having  made  a  considerable  number  of 
experiments,  I  desisted  from  it  on  account  of  the  great 
difficulties  that  occurred.  As  soon,  however,  as  I  had 
found  means  of  rendering  my  apparatus  more  perfect,  I 
formed  the  project  of  recommencing  it. 

Before  I  enter  into  the  particulars  of  my  experiments, 
I  must  say  a  few  words  respecting  the  difficulties  that 


388          On  the  Heat  developed  in  Combustion 

occurred  to  me,  even  after  I  had  my  new  apparatus,  and 
of  the  means  I  employed  to  surmount  them.  I  even 
found  myself  exposed  to  dangers,  which  it  is  necessary 
for  me  to  mention  as  a  caution  to  those  who  may  under- 
take the  same  inquiry. 

When  I  made  the  experiments  with  highly  rectified 
alcohol,  and  more  particularly  with  ether,  I  found  it  very 
difficult  to  prevent  a  portion  of  these  volatile  liquids 
from  escaping  in  the  state  of  vapour  from  the  bulk  of 
them  remaining  in  the  lamp.  I  procured  a  small  lamp, 
resembling  in  shape  a  small  round  snuff-box,  with  a  noz- 
zle rising  from  the  centre  of  the  circular  plate,  which 
closed  it  atop ;  and  on  this  plate  was  fixed  a  small  pan, 
to  hold  cold  water,  for  keeping  the  nozzle  cool  and  pre- 
venting the  heat  from  being  communicated  to  the  body 
of  the  lamp.  But  this  precaution  was  not  sufficient, 
when  I  burned  ether,  as  I  found  to  my  cost;  for,  though 
the  pan  was  twice  the  diameter  of  the  lamp,  and  filled 
with  very  cold  water,  the  water  was  so  heated  in  a  few 
minutes  that  an  explosion  took  place  from  vapour  of 
ether  kindling  in  the  air  with  a  flame  that  rose  to  the 
ceiling.  Indeed  it  was  near  setting  the  house  on  fire. 

Warned  by  this  accident,  I  procured  a  new  lamp,  much 
smaller  than  the  former,  being  only  an  inch  in  diameter 
and  three  quarters  of  an  inch  deep  ;  and  its  nozzle,  which 
was  only  two  lines  in  diameter,  was  three  quarters  of  an 
inch  high.  To  keep  this  small  lamp  cool  while  burning, 
it  was  placed  in  a  small  pan,  and  kept  constantly  im- 
mersed in  a  mixture  of  water  and  pounded  ice  to  within 
a  quarter  of  an  inch  of  the  extremity  of  the  nozzle. 
These  precautions  were  sufficient  to  prevent  any  explo- 
sion, though  not  the  evaporation  either  of  the  ether  or  of 
the  alcohol.  This  fact  I  learned  from  observing  that,  as 


and  in  the  Condensation  of  Vapours.  389 

often  as  I  made  two  consecutive  experiments  without 
filling  the  lamp  afresh,  the  alcohol  constantly  appeared 
weaker  in  the  second  experiment  than  in  the  first. 

The  cause  of  this  phenomenon  was  not  difficult  to  dis- 
cover. The  most  volatile  and  consequently  the  most 
combustible  parts  of  this  liquid,  being  diffused  in  vapour 
in  the  interior  of  the  lamp,  found  means  of  escaping 
through  the  nozzle  with  the  part  of  the  liquid  that  trav- 
.ersed  the  match,  leaving  the  alcohol  that  remained  in  the 
lamp  perceptibly  weakened. 

To  remedy  this  imperfection,  I  constructed  a  third 
lamp,  which  I  now  submit  to  the  inspection  of  the  Class. 
It  is  made  of  copper,  and  has  the  shape  of  a  small  cylin- 
dricaf  vase,  an  inch  and  a  half  in  diameter,  and  three 
inches  high,  swelling  out  a  little  atop,  and  closed  hermet- 
ically by  a  copper  stopple,  which,  being  ground  with 
emery,  fits  tight  into  the  neck  of  the  vase.  Through 
the  centre  of  this  stopple  passes  a  small  perpendicular 
hole,  which  can  be  shut  completely  or  left  a  little  open, 
as  may  be  required,  by  means  of  a  small  screw  carrying 
a  copper  collar. 

A  small  tube,  about  an  eighth  of  an  inch  in  diameter 
and  two  inches  and  a  half  long,  proceeds  horizontally 
from  the  side  of  the  vase  very  near  the  bottom.  At  the 
distance  of  an  inch  and  four  lines  from  the  vase  this  tube 
is  bent  at  a  right  angle,  rising  upwards  perpendicularly 
to  form  the  nozzle  of  the  lamp. 

This  little  tube  is  everywhere  very  thin,  except  at  its 
upper  extremity,  where  it  is  made  thicker,  to  admit  of 
being  shaped  so  as  to  fit  tight  into  a  very  small  cylindri- 
cal extinguisher,  five  lines  high  by  three  and  a  half  in 
diameter,  intended  to  close  the  nozzle  hermetically  with- 
out touching  or  deranging  the  wick,  the  moment  the 


390  On  the  Heat  developed  in  Combustion 

lamp  ceases  to  burn,  and  to  keep  it  constantly  closed 
when  the  lamp  is  not  lighted. 

Without  this  precaution,  in  experiments  made  with 
ether,  so  large  a  quantity  of  this  volatile  liquid  would 
evaporate  through  the  nozzle  of  the  lamp  while  weigh- 
ing, that  it  would  be  impossible  to  ascertain  the  quantity 
burned. 

The  nozzle  of  the  lamp  is  steadied  by  two  pieces  of 
wire,  proceeding  from  it  horizontally,  and  soldered  to  the 
body  of  the  lamp. 

To  keep  this  lamp  constantly  cold,  as  well  as  the 
liquid  it  contains,  it  is  placed  in  a  small  pan,  and  covered 
completely,  except  the  extremity  of  its  nozzle  and  that 
of  its  neck,  with  a  mixture  of  pounded  ice  and  water. 

When  the  lamp  is  weighed,  it  is  taken  out  of  the  pan, 
and  well  wiped  with  a  dry  cloth  before  it  is  put  into  the 
scale. 

When  the  lamp  is  kindled,  the  operator  must  not  for- 
get, after  it  has  burned  two  or  three  minutes,  to  open 
the  screw  that  closes  its  stopple  a  little,  though  but 
'very  little,  otherwise  it  might  go  out. 

As  the  little  horizontal  tube,  by  which  the  liquid  that 
is  burned  passes  from  the  reservoir  of  the  lamp  to  its 
nozzle,  is  always  filled  with  liquid,  so 'that  it  can  have 
no  communication  with  the  vapour  diffused  in  the  upper 
part  of  the  reservoir,  this  vapour  cannot  escape  by  the 
nozzle  of  the  lamp,  as  it  did  before  I  thought  of  this 
method  of  preventing  it. 

If  I  have  been  very  minute  in  my  description  of  this 
lamp,  it  is  because  I  thought  it  necessary  to  spare  those 
who  might  be  disposed  to  repeat  my  experiments,  or  make 
similar  ones,  all  the  difficulties  I  had  to  surmount  before 
I  found  the  means  of  having  under  command  the  com- 
bustion of  very  volatile  inflammable  liquids. 


and  in  the  Condensation  of  Vapours.          39 1 


As  the  apparatus  I  have  employed  has  now  been  de- 
scribed, it  will  be  easy  to  follow  the  steps  of  my  experi- 
ments, and  to  appreciate  their  results.  I  will  endeavour 
to  describe  them  clearly,  but  also  as  briefly  as  possible. 

Having  procured  a  stock  of  spirit  of  wine  of  the  shops, 
and  of  alcohol  of  different  degrees  of  purity,  I  ascertained 
with  the  greatest  care  their  specific  gravities  at  the  tem- 
perature of  60°  F.,  taking  that  of  water  at  the  same  tem- 
perature as  1000000.  I  chose  this  temperature  that  I 
might  afterward  the  more  easily  ascertain  the  quantities 
of  water  that  each  ought  to  contain,  according  to  the 
tables  constructed  from  the  experiments  of  M.  Lowitz. 

The  following  table  will  show  the  specific  gravity  of 
each,  and  the  quantity  of  pure  alcohol  of  Lowitz  and  of 
water  contained  in  it. 


Liquid. 

Specifi^ravity 

Composition. 

Pure  alcohol 
of  Lowitz. 

Water. 

Alcohol  of  42° 
Alcohol  of  the  shops 
Spirit  of  wine  of"  33° 

817624 
847140 
853240 

0.9179 

0.8057 
0.7788 

0.0821 
0.1943 
0.2212 

The  following  are  the  results  of  the  experiments  made 
to  ascertain  the  quantities  of  heat  which  these  liquids  fur- 
nished in  burning. 

In  three  experiments  made  with  the  spirit  of  wine  the 
quantities  of  heat  manifested  were,  — 

In  the  ist,  53.260  Ibs.  of  water  raised  from  the  temperature  of 
"       zd,    51.727    "          melting  ice  to  that  of  ebullition. 

"       3^    52-855     " 
The  mean  result  is     .         ...         •         .         .          52.614  Ibs. 

As  a  pound  of  this  liquid  contained  but  0.7788  of  the 
alcohol  considered  by  Lowitz  as  pure,  the  other  part 


392          On  the  Heat  developed  in  Combustion 

(=  o. 22 1 2)  being  only  water,  which  does  not  burn,  to  find 
how  much  water  would  be  raised  from  the  temperature 
of  melting  ice  to  that  of  ebullition  by  a  pound  of  the  pure 
alcohol  of  Lowitz,  we  have  only  to  divide  the  quantity, 
that  is,  the  measure,  of  the  mean  heat  developed  in  the 
experiments  with  the  spirit  of  wine  by  the  fraction  that 
expresses  the  quantity  of  alcohol  in  a  pound  of  this 
liquid. 

Thus,  we  have  |^  =  67.558  pounds,  the  measure  of 
the  heat  developed  in  the  combustion  of  one  pound  of 
pure  alcohol  of  Lowitz,  according  to  the  mean  result 
of  the  experiments  made  with  spirit  of  wine. 

In  two  experiments  made  with  the  alcohol  of  the  shops, 
the  mean  result  was  54.218  pounds;  and,  as  this  con- 
tained 0.8057  pound  of  pure  alcohol,  we  have  for  the 
measure  of  the  heat  developed  in  the  combustion  of 
i  pound  of  pure  alcohol  ^^  =  67.293  pounds  of  water 
heated  180°  F. 

Of  three  experiments  made  with  the  alcohol  at  42°,  the 
mean  result  was  61.952  pounds  of  water  heated  180°  F. 
by  the  heat  developed  in  the  combustion  of  one  pound 
of  this  liquid. 

Hence,  I  pound  of  pure  alcohol  should  furnish  heat 
enough  in  burning  to  raise  67.57  pounds  of  water  180° 
F.;  for  £Hf  =  67.101. 

Taking  the  mean  between  the  results  of  these  eight 
experiments  with  three  alcoholic  liquors,  we  shall  have 
for  the  measure  of  the  heat  developed  in  the  combustion 
of  one  pound  of  pure  alcohol  of  Lowitz  67.317  pounds 
of  water  raised  from  the  temperature  of  melting  ice  to 
that  of  ebullition. 

It  will  be  extremely  interesting,  no  doubt,  to  know 
whether  this  quantity  of  heat  agree  with  the  quantities 


and  in  the  Condensation  of  Vapours.  393 

of  combustible  matter  (carbon  and  hydrogen)  in  alcohol. 
We  will  see. 

According  to  the  analysis  of  M.  de  Saussure,  i  pound 
of  the  alcohol  of  Lowitz  contains 

Carbon 0.4282  Ib. 

Free  hydrogen     .         .         .         .         .         .         .         0.1018 

Water 0.4700 


Now,  according  to  the  calculations  of  Dr.  Crawford, 
we  shall  have  for  the  measure  of  the  heat  developed  in 
the  combustion  of 

0.4282  Ib.  of  carbon         .          24.667  Ibs.  of  water  heated  180°  F. 
0.1018  Ib.  of  hydrogen         .     41.738    "  "         "  " 


Total     ....         66.405    "  "         "  " 

The  experiments  gave  us     .     67.317    "  "         "  " 

It  is  rare  in  a  research  of  such  delicacy  to  find  the  re- 
sults of  experiment  agree  so  perfectly  with  those  of  cal- 
culation. 


SECTION  IV.  —  Heat  developed  in  the  Combustion  of  Sul- 
phuric Ether. 

I  have  already  mentioned  the  difficulties  which  I 
overcame  before  being  able  to  regulate  the  combus- 
tion of  this  substance  in  such  a  way  as  to  render  the 
results  of  my  experiments  regular  and  satisfactory  ;  but 
I  met  with  still  further  difficulties  in  the  course  of  this 
delicate  inquiry. 

As  alcohol  is  necessarily  employed  in  making  sulphuric 
ether,  and  as  these  two  liquids  may  be  united  in  any 
proportions,  it  is  extremely  difficult,  if  not  impossible, 


394 


the  Heat  developed  hi  Combustion 


to  separate  them  entirely  ;  and  as  both  are  colourless  and 
limpid,  either  when  mixed  or  separate,  we  can  scarcely 
judge  of  the  degree  of  purity  of  the  ether,  except  by  its 
specific  gravity,  and  even  in  this  way  but  very  imperfectly. 

The  most  highly  rectified  sulphuric  ether  which  I  could 
procure,  and  which  I  employed  in  my  experiments,  was 
prepared  in  M.  Vauquelin's  laboratory.  Its  specific 
gravity  is  728.34  at  the  temperature  of  16°  Reaumur. 
As  that  which  was  employed  by  M.  de  Saussure  in  his 
analysis  was  only  of  the  specific  gravity  of  717  at  the 
same  temperature,  by  regarding  the  ether  which  I  em- 
ployed as  being  a  mixture  of  the  same  degree  of  purity 
with  that  of  M.  de  Saussure,  and  the  pure  alcohol  of 
Lowitz  having  a  specific  gravity  of  792,  we  shall  find, 
upon  making  a  calculation,  that  the  ether  which  I  em- 
ployed was  a  mixture  of  85  parts  of  ether  of  the  spe- 
cific gravity  of  717,  and  15  parts  of  pure  alcohol  of  Lo- 
witz of  the  specific  gravity  of  792. 

On  burning  this  mixture  under  my  calorimeter,  after 
having  brought  my  apparatus  to  the  highest  degree  of 
perfection,  I  obtained  the  following  results  :  — 


Duration  of  the  ex- 
periment. 

Ether  burned. 

Quantity  of  water 
heated. 

Temper 
water 

ature  of 
n  the 
meter 

il 

1 

wf 

•5 

1 

H 

Result. 

I 

Quantity  of  water  ! 
heated    180°    of  i 
Fahrenheit  with  ' 
the  heat  devel- 
oped in  the  com-  ! 
bustion    of  one  , 
pound     of    the  [ 
combustible. 

At  the  com- 
mencement. 

^|6 

m.       s. 
II 
II     15 

9 

20 

22 

Grms. 
I.96 
2.01 
2. 

3-29 

3.06 

Grms. 
2781 

Degrees. 
54i 

58| 

lei 

Degrees. 

69! 
731 

Degrees. 

ioi-°F. 

I0t 

17 

16 

Degrees 

60°  F. 
60 
60 
61 

79.996 
80.710 
80.146 
79.884 
80.784 

Mean  result  of  the  five  experiments                                         80.304 

and  in  the  Condensation  of  Vapours.  395 

Continuing  to  make  use  of  the  estimates  of  Crawford, 
for  the  quantities  of  heat  developed  in  the  combustion  of 
hydrogen  and  carbon,  we  shall  see  if  these  estimates  are 
sufficient  to  account  for  the  heat  manifested  in  these  five 
experiments. 

As  the  ether  employed  was  a  mixture  of  15  parts  of 
pure  alcohol  of  Lowitz,  and  85  parts  of  ether  of  the 
specific  gravity  of  717  at  the  temperature  of  16°  Reau- 
mur, and  consequently  similar  to  the  ether  analyzed  by 
M.  de  Saussure,  we  shall  begin  by  determining  the  quan- 
tity of  heat  which  ought  to  be  developed  in  the  combus- 
tion of  these  fifteen  parts  of  alcohol. 

As  M.  de  Saussure  has  shown  that  in  one  pound  of 
Lowitz's  alcohol  (of  the  specific  gravity  of  792)  there 
are  0.4282  pound  of  carbon  and  0.1068  pound  of  free 
hydrogen,  we  ought  to  find  in  0.15  pound  of  this  same 
liquid  0.06423  pound  of  carbon,  and  0.01527  of  free 
hydrogen. 

According  to  the  estimate  of  Crawford,  0.06423  pound 
of  carbon  ought  to  furnish  a  sufficiency  of  heat  in  its 
combustion  to  raise  the  temperature  of  3.7002  pounds 
of  water  180°  F.  ;  and  0.01527  pound  of  hydrogen 
ought  to  furnish  enough  to  raise  6.2607  pounds  of 
water  the  same  number  of  degrees  ;  and  these  two  quan- 
tities of  water,  making  together  9.9609  pounds,  afford 
a  measure  of  the  quantity  of  heat  which  must  be  devel- 
oped in  the  combustion  of  the  15  parts  of  alcohol, 
which  are  found  mixed  with  85  parts  of  ether,  in  order 
to  form  the  combustible  liquid  employed  under  the 
name  of  sulphuric  ether  in  my  experiments. 

Now,  as  one  pound  of  this  mixed  liquid  has  furnished 
in  its  combustion  enough  of  heat  to  raise  80.304 
pounds  of  water  180°  F.,  if  we  deduct  from  this  mass 


396  On  the  Heat  developed  in  Combustion 

the  quantity  of  water  which  the  15  per  cent  of  alcohol 
must  heat  (=  9.909),  that  which  remains  (=  70.3431 
pounds  of  water)  will  be  the  measure  of  the  quantity  of 
heat  developed  in  the  combustion  of  85  per  cent  of 
ether  of  the  gravity  of  717,  which  exists  in  this  com- 
bustible liquid. 

According  to  the  analysis  of  sulphuric  ether  made  by 
M.  d.e  Saussure,  we  ought  to  find  in  one  pound  of  this 
liquid  (of  the  specific  gravity  of  717) 

Carbon 0.590  Ib. 

Free  and  combustible  hydrogen     .          .          .          .         0.194 
Oxygen  and  hydrogen  in  the  proportions  necessary  to 

form  water  .         .         .         ,  .0.216 


Consequently,  we  ought  to  find  in  0.85  pound  of  the 
same  kind  of  ether  the  following  quantities  of  combus- 
tible substances,  viz.  :  — 

Carbon         .         .     "    .         .         ...         .     0.5015  Ib. 

Free  and  combustible  hydrogen  .          .          .         0.1651 

We  shall  now  see  if  these  quantities  of  combustible 
substances  are  sufficient  to  account  for  the  heat  which  is 
manifested  in  our  experiments. 

The  0.5015  pound  of  carbon  ought  to  furnish  suf- 
ficient heat  to  raise  28.89  pounds  of  water  180°  F. ; 
and  the  0.1651  pound  of  hydrogen  sufficient  to  heat 
67.64  pounds  the  same  number  of  degrees. 

These  two  masses  of  water  form  together  96.53 
pounds  ;  but  we  shall  see  that  the  quantity  of  heat  fur- 
nished by  the  85  parts  of  ether  in  the  experiments  can- 
not be  greater  than  that  which  is  necessary  to  heat 
70.3431  pounds  of  water  180°  F. 

As  the  experiments  have  been  made  with  the  greatest 


and  in  the  Condensation  of  Vapours.          397 

care,  and  frequently  repeated,  and  always  with  very  uni- 
form results ;  and  as  the  estimates  which  we  have  adopted, 
with  respect  to  the  quantities  of  heat  which  are  developed 
in  the  combustion  of  hydrogen  and  in  that  of  carbon, 
have  been  confirmed  so  as  to  leave  little  doubt  upon  this 
subject,  —  upon  investigating  the  cause  of  the  great  differ- 
ence between  the  quantity  of  heat  actually  developed  in 
the  combustion  of  the  85  parts  of  sulphuric  ether  burned 
in  the  experiments  which  we  have  examined,  and  the 
quantity  given  by  calculation,  we  are  compelled,  in  my 
opinion,  to  admit  that  there  is  an  error  in  the  analysis 
of  this  liquid,  and  that  it  does  not  contain  so  much  free 
and  inflammable  combustible  matter  as  M.  de  Saussure 
ascribes  to  it. 

As  it  seems  to  me  to  be  much  more  probable  that  an 
error  has  been  committed  in  determining  the  quantity  of 
free  hydrogen  in  this  substance  than  in  determining  the 
quantity  of  carbon,  I  shall  suppose  with  M.de  Saussure 
that  there  is  really  in  one  pound  of  sulphuric  ether  (of  the 
specific  gravity  of  717)  0.59  of  carbon  ;  but  instead  of 
estimating  the  quantity  of  free  hydrogen  in  this  liquid 
according  to  the  results  of  M.  de  Saussure,  I  shall  adopt 
the  estimate  of  Mr.  Cruickshanks. 

This  excellent  chemist  concluded,  from  his  experi- 
ments, that  in  the  vapour  of  sulphuric  ether  the  carbon 
is  to  the  hydrogen  as  5  to  i. 

In  the  0.85  pound  of  sulphuric  ether  (specific  gravity 
717)  which  were  mixed  with  the  0.15  pound  of  alcohol, 
in  order  to  form  one  pound  of  the  mixed  liquid  employed 
in  my  experiments,  there  were  0.5015  pound  of  carbon  ; 
and  dividing  this  number  by  5,  we  shall  see  that  this 
carbon  ought  to  be  united  with  0.1003  pound  of  free 
hydrogen,  instead  of  being  united  with  0.1651  pound,  as 
we  shall  suppose  according  to  M.  de  Saussure. 


398  On  the  Heat  developed  in  Combustion 

Let  us  now  see  if,  by  adopting  the  analysis  of  Mr. 
Cruickshanks  with  respect  to  the  hydrogen,  instead  of 
that  of  M.  de  Saussure,  the  calculation  will  agree  better 
with  the  experiment. 

We  have  seen  that  the  quantity  of  water  heated 
1 80°  Fahrenheit,  which  represents  the  quantity  of 
heat  which  must  be  developed  in  the  combustion 
of  the  0.15  Ib.  of  alcohol,  was  .  .  .  9.9609  Ibs. 

And  that  the  quantity  answering  to  0.5015  Ib.  of 

carbon,  which  exists  in  the  0.85  of  ether,  was  .  28.89 

We  shall  for  the  present  add  that  which  answers 
to  the  combustion  of  0.1003  Ib.  of  free  combus- 
tible hydrogen,  which,  according  to  Mr.  Cruick- 
shanks, ought  to  be  found  united  to  this  quantity 
of  carbon  in  order  to  form  the  ether  .  .  41.123 


These  three  quantities  of  water  together  are  the 
measure  of  the  heat  which  must  be  developed  in 
the  combustion  of  one  pound  of  sulphuric  ether  of 
the  kind  employed  in  my  experiments  .  .  79-9739 

The  mean  result  of  five  experiments  was    .         .         80.304. 

This  coincidence  between  the  calculation  and  the  ex- 
periment is,  doubtless,  too  remarkable  to  be  owing  to 
chance  ;  but  I  am  ready  to  prove  that  it  occurred  without 
being  foreseen  or  expected. 

From  all  these  results  we  may  conclude,  that  one  pound 
of  sulphuric  ether,  of  the  specific  gravity  717  at  the 
temperature  of  16°  Reaumur,  or  of  the  same  species 
with  that  employed  by  M.  de  Saussure,  should  have 
furnished  in  combustion  enough  of  heat  to  raise  82.369 
pounds  of  water  180°  F.,  viz.  :  — 

That  furnished  by  0.59  Ib.  of  carbon      .         .         .     33.989  Ibs. 
And  that  furnished  by  0.118  Ib.  of  hydrogen         .         48.380 

82.369 


and  in  the  Condensation  of  Vapours.          399 

If  the  proportion  of  free  hydrogen  in  the  ether  ana- 
lyzed by  M.  de  Saussure  was  really  such  as  he  has  deter- 
mined it  to  be,  one  pound  of  this  liquid  ought  to  furnish 
a  sufficiency  of  heat  in  its  combustion  to  raise  113.566 
pounds  of  water  180°  F.,  viz.  :  — 

That  furnished  by  0.59  Ib.  of  carbon      .         .          .     33.989  Ibs. 
And  that  which  was  furnished  by  0.194091  of  hy- 
drogen         79-577 


113.566 

But  I  can  the  less  persuade  myself  that  this  liquid  can 
furnish  in  its  combustion  so  much  heat,  because  one 
pound  of  white  wax  furnished  no  more  than  what  was 
sufficient  to  heat  94.682  pounds  of  water  the  same  num- 
ber of  degrees. 

According  to  the  analysis  of  M.  de  Saussure,  100  parts 
of  sulphuric  ether,  of  the  specific  gravity  of  717,  at  16° 
Reaumur,  are  composed  of 

Carbon 59  parts 

Hydrogen 22 

Oxygen 19 


Supposing  that  the  19  parts  of  oxygen  are  combined 
with  3.6  parts  hydrogen,  so  as  to  form  with  them  21.6 
parts  water,  100  parts  of  this  kind  of  ether  ought  to  be 
composed  of 

Carbon      .........     59 

Free  and  combustible  hydrogen         ....          19.4 

Consequently,  inflammable  substances  .         .         .     78.4 

Water   .  21.6 


400  On  the  Heat  developed  in  Combustion 

From  the  result  of  my  experiments,  100  parts  of  this 
kind  of  ether  ought  to  be  composed  of 

Carbon      .........     59 

Free  or  combustible  hydrogen  ....          n.8 


Consequently,  combustible  substances           .         .         .     70.8 
Water   . 29.2 

100 

Or,  reducing  the  water  to  its  elements,  — 

Carbon     .........     59 

Hydrogen,  free  or  combustible        .         .         .    .     11.8 

Ditto,  non-combustible         ....  3.5 

15.3 

Oxygen          .         .         .         •         .         .         .         .         25.7 

100 

According  to  M.  de  Saussure's  analysis,  as  well  as  from 
the  results  of  my  experiments,  100  parts  of  pure  alcohol 
of  Lowitz,  qf  the  specific  gravity  of  792,  at  the  temper- 
ature of  1 6°  Reaumur,  are  composed  of 

Carbon  »         »  -.         .         .         .         .          42.82 

Free  or  combustible  hydrogen      .         ..       ..        .         .      10.18 

Consequently,  combustible  substances       .          .         .          53 
Water  . 47 

100 

Or,  reducing  the  water  to  its  elements,  100  parts  of 
this  alcohol  are  composed  of 

Carbon  .          . 42.82 

Hydrogen,  combined  and  non-combustible    .  5.64 

Hydrogen,  combustible   .         ...        .         .     10.18 

15.82 

Oxygen  .         .         .         .'-•'.         .         .         41.36 


and  in  the  Condensation  of  Vapours.  40 1 

By  supposing  that  water  exists  completely  formed  both 
in  alcohol  and  ether,  the  constituent  parts  of  these  two 
liquids  would  be,  according  to  the  results  of  our  inquiries, 

Alcohol.  Ether. 

Carbon 42.82  59 

Combustible  hydrogen  ....      10.18  11.8 

Water       .......          47  29.2 


The  elements  of  water  exist  most  assuredly  both  in  al- 
cohol and  ether  ;  but  there  is  good  reason  to  believe  that 
water  does  not  exist  in  its  natural  state  of  condensation 
in  these  two  substances,  neither  when  they  are  in  a  state 
of  liquidity,  nor  when,  being  sufficiently  heated,  they  are 
transformed  into  elastic  fluids. 

When  we  mix  water  with  alcohol,  there  is  a  consider- 
able change  both  in  temperature  and  volume,  which  in- 
dicates a  new  arrangement  of  elements,  or  a  chemical 
action  ;  and  what  proves  in  a  still  more  certain  manner 
that  this  action  has  taken  place,  the  liquid  which  results 
from  this  mixture  may  be  distilled,  i.  e.  vaporized  by 
heat,  and  afterwards  condensed,  without  being  decom- 
posed :  but  it  is,  above  all,  in  the  little  heat  which  is  de- 
veloped in  the  condensation  of  the  vapour  of  alcohol  and 
ether  that  we  discover  certain  proofs  that  the  oxygen  and 
hydrogen  which  exist  as  elements  in  these  liquids  do  not 
exist  in  the  state  of  water.  I  shall  recur  to  this  subject 
again. 

SECTION    V.  —  On    the   Quantity   of  Heat   developed  in 
the  Combustion  of  Naphtha. 

The  naphtha  which  I  made  use  of  in  my  experiments 
was  supplied  by  M.  Vauquelin  :  it  had  been  purified  by 

VOL.    II.  26 


402  On  the  Heat  developed  in  Combiistion 

distillation,  and  its  specific  gravity  at  the  temperature  of 
56°  F.  was  827.31. 

The  following  are  the  details  and  results  of  two  ex- 
periments made  with  this  liquid  on  the  29th  of  January, 
1812. 

The  capacity  of  the  calorimeter  for  heat  was  equal  to 
that  of  2781  grammes  of  water. 


Duration 
of  the 
experiment. 

Quantity  of 
naphtha 
burned. 

Elevation  of 
the  tempera- 
ture of  the 
calorimeter    in 
degrees  of 
Fahrenheit. 

Result. 

Pounds  of  water  heat- 
ed 180°  with  i  Ib.  of 
this  substance. 

ist  Experiment 
2d  Experiment 

32 
36 

Grammes. 

4-45' 

2.77 

Degrees. 

i6°F. 

I2f 

Ibs. 
73.881 

72.77! 

Mean  result                                                                              73.3  76 

The  naphtha  was  burned  in  the  same  small  lamp 
which  I  had  employed  in  my  experiments  made  with 
alcohol  and  sulphuric  ether;  but  as  I  had  not  been  able 
to  succeed  in  burning  the  naphtha  without  smoke,  I 
cannot  rely  implicitly  upon  the  results  of  these  experi- 
ments. Perhaps  with  pure  oxygen  gas  we  might  succeed 
in  burning  it  entirely. 

I  have  met  with  the  same  difficulty  in  burning  oil  of 
turpentine  and  colophon  ;  and  for  this  reason  I  thought 
it  would  be  useless  to  detail  my  experiments  with  these 
two  substances. 


SECTION  VI.  —  On  the  Quantity  of  Heat  developed  in  the 
Combustion  of  Tallow. 

Having  procured  tallow  candles  of  a  good  quality, 
those  which  are  called  six  in  the  pound \  I  burned  one  un- 
der the  calorimeter,  taking  care  to  keep  it  well  snuffed, 
in  order  to  avoid  smoke. 


and  in  the  Condensation  of  Vapours.          403 


The  following  are  the  details  and  results  of  two  ex- 
periments made  on  the  same  day  (i6th  of  November, 
1811)  with  one  of  these  candles. 

The  capacity  of  the  calorimeter  for  heat  was  equal  to 
that  of  2371  grammes  of  water. 


Time  while  the 
candle  was 
burning  under 
the  calorim- 
eter. 

Quantity  of 
tallow   burned. 

Elevation  of 
the  tempera- 
ture ofthe 
water  in  the 
calorimeter. 

Result. 

Quantity  of  water 
heated  180°  with  the 
heat  developed  in  the 
combustion  of  i  Ib.  of 
tallow. 

1st  Experiment 
zd   Experiment 

m.       s. 

16     2 
16  50 

Grammes. 

1.6 

i-7 

lo^F. 

io* 

Ibs. 
84.385 
82.991 

Mean  result      .         .         . 
We  have  seen  that  with  white  wax  the  result  was  . 
With  purified  rape  oil        ..... 
And  with  olive  oil          

.       83.688 
94-682 

•     93-°73 
90.439 

SECTION  VII.  —  Quantity  of  Heat  developed  in  the  Com- 
bustion of  Charcoal. 

If  we  could  burn  under  the  calorimeter  some  pieces 
of  wood  made  into  charcoal  with  the  same  facility  that  we 
burn  thin  pieces  of  dry  wood,  the  investigation  in  ques- 
tion would  not  be  attended  with  difficulty ;  but  the 
charcoal  cannot  be  burned  in  this  manner.  We  can 
light  a  piece  of  charcoal  very  well,  and  if  it  be  very  thin 
it  continues  to  burn  until  it  is  entirely  consumed  ;  but 
the  combustion  is  so  slow,  and  furnishes  so  little  heat, 
that  it  would  require  several  hours  to  heat  the  calorim- 
eter sufficiently  to  give  an  appreciable  result ;  and  for 
this  single  reason  the  result  could  not  but  be  extremely 
uncertain. 

I  have  long  endeavoured,  but  without  success,  to  find 


404  On  the  Heat  developed  in  Combustion 

a  method,  by  steeping  thin  chips  of  wood  in  some  in- 
flammable liquid,  to  burn  the  charcoal  more  rapidly. 

Some  chips  of  wood  of  a  known  weight,  perfectly 
dried  and  strongly  heated,  were  plunged  into  white  wax, 
melted  and  very  hot,  and  the  chips,  when  taken  out  and 
cooled,  were  again  weighed. 

Their  augmentation  in  weight  gave  me  the  quantity 
of  wax  which  they  had  imbibed  ;  and  as  I  knew  accu- 
rately how  much  heat  this  quantity  of  wax  should  have 
given  in  its  combustion,  if  the  chips  thus  prepared  had 
been  burned  properly  under  the  calorimeter,  I  should 
certainly  have  discovered  how  much  heat  the  charcoal 
would  have  furnished  ;  but  the  experiment  did  not  suc- 
ceed. 

The  wax  was  entirely  burned,  and  the  chip  of  wood 
became  very  red  ;  but  it  was  not  burned,  at  least  not  en- 
tirely, nor  in  such  a  way  as  to  give  me  the  least  hope  of 
being  able  to  derive  any  advantage  from  my  experi- 
ment ;  and  I  did  not  succeed  any  better  by  steeping  my 
chips  of  charcoal  in  melted  tallow,  in  oil,  alcohol,  sul- 
phuric ether,  naphtha,  essential  oil  of  turpentine,  in  a 
solution  of  gum-arabic,  and  in  that  of  sugar.  I  have 
also  tried  colophon,  but  without  more  success. 

I  have  made  several  experiments  in  order  to  deter- 
mine directly  the  quantity  of  heat  which  is  developed 
in  the  combustion  of  considerable  masses  of  charcoal 
(80  grammes)  burned  in  a  small  stove,  under  a  calorime- 
ter of  a  large  size,  which  I  procured  at  Paris  four  years 
ago,  and  which  I  have  still  in  my  laboratory  ;  but  the 
results  of  these  experiments  have  been  too  variable  to 
satisfy  myself. 

After  all  the  care  which  I  took,  I  found  that  the  ex- 
periments of  Crawford  were  better  than  mine ;  and  as 


and  in  the  Condensation  of  Vapours.          405 

they  furnished  more  heat  than  I  could  find,  I  have  not 
hesitated  to  adopt  their  results  instead  of  relying  upon 
my  own. 

SECTION  VIII.  —  Quantities  of  Heat  developed  in  the  Com- 
bustion of  Wood. 

In  a  memoir  which  I  had  the  honour  to  present  to  the 
Class  on  the  9th  of  September,  1812,  I  gave  an  account 
of  a  considerable  number  of  experiments  (upwards  of 
fifty)  which  I  made  in  order  to  determine  the  quantities 
of  heat  which  are  developed  in  the  combustion  of  dif- 
ferent kinds  of  wood. 

From  the  results  of  these  experiments,  it  appears 
that,  at  equal  weights,  the  light  and  soft  woods  give 
out  a  little  more  heat  than  the  compact  and  heavy 
woods  ;  but  as  the  difference  is  very  small,  we  may 
rather  ascribe  it  to  a  greater  degree  of  humidity  in  the 
latter. 

It  is  certain  that  the  compact  retain  humidity  with 
more  tenacity  than  the  light  woods,  and  a  small  dif- 
ference in  the  dryness  of  a  wood  ought  to  produce  a 
sensible  effect  on  its  apparent  weight,  and  consequently 
upon  the  result  of  the  calculations  which  we  employ  in 
order  to  determine  the  heat  which  it  furnishes. 

In  physical  and  chemical  researches,  it  is  always  satis- 
factory to  be  able  to  compare  the  results  of  new  experi- 
ments with  those  of  more  ancient  date,  particularly 
when  the  latter  have  been  made  by  persons  remarkable 
for  their  accuracy. 

M.  Lavoisier  has  shown  that  equal  quantities  of  heat 
are  produced  in  the  combustion  of  1089  parts  in  weight 
of  oak,  and  600  parts  of  charcoal ;  consequently  equal 


406  On  the  Heat  developed  in  Combustion 


quantities  of  heat  ought  to  be  furnished  in  the  com- 
bustion of  one  pound  of  oak  and  0.55  of  a  pound  of 
charcoal. 

According  to  the  experiments  of  Dr.  Crawford,  one 
pound  of  charcoal  furnishes  in  its  combustion  enough 
of  heat  to  raise  the  temperature  of  57.608  pounds  of 
water  180°  of  F. 

Consequently  the  temperature  of  31.684  pounds  of 
water  would  be  raised  the  same  number  of  degrees  by 
the  heat  furnished  in  the  combustion  of  0.55  pound  of 
charcoal. 

According  to  the  result  of  the  experiments  of  M. 
Lavoisier,  this  same  quantity  of  heat  ought  to  be  fur- 
nished in  the  combustion  of  one  pound  of  oak. 

Having  made  four  consecutive  experiments  with 
very  good  dry  oak  wood,  and  in  very  thin  slips,  burned 
so  as  to  give  out  neither  smoke  nor  smell,  and  which 
left  but  an  inappreciable  quantity  of  ashes  and  no  char- 
coal, I  obtained  the  following  results  :  — 


Number  of 
experiments. 

Quantity  of  wood 
burned. 

Elevation  of  the 
temperature  of 
the  calorimeter. 

Result. 

Pounds  of  water  heated  180° 
with  one  pound  of  combustible. 

2 

3 
4 

Grammes. 
5.10 

5-13 
5.12 

4-95 

Degrees. 

ioj°  F. 
10* 

I  Of 
10 

Ibs. 
31.051 
31-623 

3I-94I 
31.212 

Mean  r< 
Result 
expei 

according   to  Lavoisier  and   Crawford's  }            ^ 
iments  ...                                               j           ' 

It  is  rare  to  find  experiments  made  by  different  per- 
sons at  distant  periods,  and  with  very  different  appara- 
tus, which  agree  better  together. 

But  experiments  which  are  well  made  can  never  fail 


and  in  the  Condensation  of  Vapours.          407 

in  agreeing  in  their  results,  whatever  be  the  difference 
of  the  methods  employed :  it  is,  nevertheless,  necessary 
to  remark,  that  the  coincidence  in  question  could  not 
be  so  perfect  as  it  appears,  for  everything  depends  upon 
the  equality  of  the  humidity  which  may  exist  in  the 
wood  and  charcoal  employed,  —  a  circumstance  which  it 
is  impossible  to  establish. 

SECTION  IX.  —  On  the  greatest  Intensity  of  Heat  which 
it  is  possible  to  produce  by  the  Combustion  of  inflammable 
Substances. 

It  is  well  known  that  the  heat  of  a  small  fire  seems  to 
be  less  intense  than  that  of  a  large  fire,  even  when  the 
same  species  of  combustible  is  employed  ;  but  I  do  not 
know  that  it  has  been  attempted  to  determine  the  limits 
of  the  intensity  of  a  fire,  or  the  greatest  degree  of 
heat  which  it  is  possible  to  produce  by  means  of  com- 
bustion. 

In  order  to  elucidate  this  subject,  it  is  necessary  to 
consider  attentively  what  passes  in  the  chemical  opera- 
tion which  we  call  combustion. 

In  all  known  cases  where  two  elementary  substances 
unite  together  so  as  to  form  a  new  substance,  there,  is  a 
change  of  temperature,  so  that  the  new  substance  at 
the  moment  of  its  formation  has  a  temperature  differing 
strongly  from  that  of  the  surrounding  bodies.  Conse- 
quently, the  surrounding  bodies  are  always  either  heated 
or  cooled  more  or  less  by  the  new  body  which  has  been 
formed. 

But  in  order  that  this  effect  may  be  sensible  to  our 
organs,  or  capable  of  acting  in  a  sensible  manner  upon 
our  apparatus,  it  is  necessary  that  the  quantity  of  the 


408          On  the  Heat  developed  in  Combustion 

new  substance  formed  should  be  considerable  ;  for  it  is 
certain  that  the  most  intense  heat,  if  it  be  developed  in 
a  very  small  particle  of  matter,  may  exist  without  pro- 
ducing any  sensible  effect  which  could  give  us  any  indi- 
cations of  its  existence. 

It  is  not  less  true  that  the  chemical  union  of  two 
atoms,  two  different  elementary  substances,  ought  al- 
ways, under  every  circumstance,  to  be  accompanied  with 
one  and  the  same  change  of  temperature  ;  for  this  union 
takes  effect  in  a  place  so  distant,  relative  to  all  the 
other  bodies  (if,  in  every  case,  all  the  interstices  are  not 
filled  with  particles  of  an  ethereal  fluid),  that,  we  can- 
not conceive  how  the  change  of  temperature  in  question 
may  be  either  augmented  or  diminished  by  the  effect 
of  the  action  of  these  surrounding  bodies. 

It  is  extremely  probable,  from  what  we  have  been 
able  to  remark  in  a  great  number  of  phenomena,  that 
the  approximation  of  the  elementary  particles  of  bodies 
is  always  accompanied  by  an  elevation  of  their  tempera- 
ture;  and  as  there  cannot  be  new  substances  formed  ex- 
cept in  consequence  of  an  approximation  and  the  chem- 
ical union  of  elementary  particles,  we  may  conclude 
that  there  cannot  be  new  chemical  compositions  without 
a  development  of  heat. 

We  may  form  an  idea  of  what  passes  in  combustion, 
by  considering  the  phenomena  which  take  place  when 
water  freezes. 

At  a  certain  temperature,  which  is  invariable,  the 
molecules  of  the  liquid  are  disposed  to  approximate  in 
order  to  form  a  solid  body,  ice ;  and  the  first  particle 
of  ice  which  is  formed  is  accompanied  by  a  develop- 
ment of  a  certain  quantity  of  heat,  which  quantity  is 
invariable. 


and  in  the  Condensation  of  Vapours.  409 

It  is  also  very  probable  that  it  is  at  a  temperature 
which  is  invariable  that  the  oxygen  and  hydrogen  are 
disposed  to  approximate  and  unite  in  order  to  form  an 
atom  of  vapour,  and  that  the  intensity  of  the  heat  devel- 
oped at  the  moment  of  this  union  is  also  invariable,  and 
that  it  is  always  manifested  in  all  its  intensity  in  the 
atom  of  vapour  which  is  formed. 

But  as  the  atom  of  vapour  is  extremely  small,  and  sur- 
rounded by  bodies  relatively  very  cold,  its  heat  is  soon 
dissipated. 

There  is,  however,  a  method,  which  appears  certain, 
that  we  .may  employ  in  order  to  determine  the  tempera- 
ture of  an  atom  of  vapour  at  the  moment  of  its  forma- 
tion, and  by  this  means  we  may  know  what  is  the  high- 
est temperature  which  it  is  possible  to  procure  by  means 
of  combustion. 

We  have  seen  that,  according  to  the  results  of  the 
researches  of  Dr.  Crawford,  it  seems  that  when  i 
pound  of  hydrogen  is  burned,  enough  of  heat  is  de- 
veloped on  this  occasion  to  elevate  the  temperature 
of  410  pounds  of  water  180°  F.  (=  100  degrees  cen- 
tigrade). 

Now  as  i  pound  of  hydrogen  perfectly  dry  is  united 
by  burning  to  7.3333  pounds  of  oxygen,  and  forms 
with  it  8.3333  pounds  of  steam,  it  is  evident  that 
the  quantity  of  heat  which  exists  in  8.3333  pounds  of 
steam  at  the  instant  when  this  steam  is  formed,  is 
equal  to  that  which  is  necessary  to  raise  the  temperature 
of  410  pounds  of  water  180°  F.,  or  to  elevate  the  tem- 
perature of  73,800  pounds  of  water,  one  degree  of  the 
scale  of  Fahrenheit. 

From  this  calculation  we  may  conclude  that  the  quan- 
tity of  heat  which  exists  in  i  pound  of  steam,  at  the 


4io          On  the  Heat  developed  in  Combiistion 

instant  when  it  is  formed,  is  sufficient- to  raise  the  tem- 
perature of  i  pound  of  water  10,063  degrees. 

If  the  capacity  of  the  steam  for  heat  was  equal  to  that 
of  liquid  water,  it  is  very  certain  that  the  temperature 
of  the.  vapour  at  the  instant  of  its  formation  would  be 
that  of  10,063°  F. 

In  order  to  form  an  idea  of  this  degree  of  intensity, 
we  may  compare  it  to  an  intensity  of  heat  which  is 
known. 

A  piece  of  iron  heated  until  it  becomes  red  even  in 
daylight  has  then  the  temperature  of  1000°  F.  ;  con- 
sequently the  temperature  of  the  steam  at  the  instant 
of  its  formation  would  be  ten  times  higher  than  that  of 
red-hot  iron  :  but  as,  according  to  Crawford,  the  capa- 
city of  the  steam  for  heat  is  greater  than  that  of  water 
in  the  proportion  of  1.55  to  i,  the  temperature  in  ques- 
tion will  be  less  than  that  of  10,063°  i°  tne  same  pro- 
portion. It  will  therefore  be  equal  to  8750°  F. 

Here,  therefore,  is  the  limit  of  the  intensity  of  the 
heat  in  the  midst  of  the  greatest  fire,  in  which  pure 
hydrogen  would  be  employed  as  a  combustible,  and  in 
which  the  fire  would  be  fed  by  pure  oxygen.  This  is  an 
intensity  which  we  may  approach  more  or  less,  but  which 
we  can  never  attain. 

As  Wedgwood's  pyrometer  indicates  much  higher 
temperatures,  it  seems  demonstrated  by  the  result  of 
this  calculation  that  the  scale  of  this  pyrometer  is  faulty. 
These  doubts  have  been  stated  by  other  chemists. 

But  in  order  to  decide  definitively  upon  this  inter- 
esting question,  it  would  be  indispensably  necessary  to 
know  accurately  the  capacity  of  steam  for  heat  at  different 
temperatures;  a  thing  unknown,  and  which  is  difficult  to 
determine. 


and  in  the  Condensation  of  Vapours.          4 1 1 

Upon  examining  the  subject  attentively,  we  shall 
find,  however,  reasons  for  thinking  that  the  capacity  of 
steam  for  heat  ought  necessarily  to  be  diminished  with 
the  increase  of  its  temperature.  The  following  calcula- 
tions may  serve  to  elucidate  this  subject. 

In  order  to  determine  the  highest  degree  of  tempera- 
ture which  can  exist  in  the  midst  of  the  greatest  fire 
when  pure  hydrogen  is  the  only  combustible  employed 
and  when  the  fire  is  fed  by  atmospheric  air,  it  is  necessary 
to  remark  that,  as  oxygen  and  nitrogen  are  intimately 
mixed  in  the  atmosphere,  the  heat  which  results  from 
the  combustion  of  hydrogen  ought  to  be  immediately 
divided  between  the  vapour  which  results  from  the 
union  of  the  hydrogen  with  the  oxygen,  and  the  nitro- 
gen which  is  found  necessarily  mixed  with  this  vapour. 

In  order  to  simplify  our  inquiry,  we  shall  commence 
by  supposing  that  all  the  oxygen  which  exists  in  the 
atmospheric  air  is  employed. 

In  this  case,  as  it  requires  7.3333  pounds  of  oxy- 
gen to  be  united  to  i  pound  of  hydrogen  in  order  to 
compose  8.3333  pounds  of  steam,  and  as  the  atmos- 
pheric air  is  composed  of  21  pounds  of  oxygen  gas 
mixed  with  79  pounds  of  nitrogen,  the  7.3333  pounds 
of  oxygen  which  are  united  to  i  pound  of  hydrogen  in 
order  to  form  8.3333  pounds  of  steam,  ought  to  be 
found  mixed  with  27.587  pounds  of  nitrogen  ;  conse- 
quently the  heat  developed  in  the  combustion  of  i 
pound  of  hydrogen  ought  to  be  also  divided  between 
8.3333  pounds  of  steam  and  27.587  pounds  of  nitro- 
gen ;  and  this  partition  ought  to  take  place  in  the 
direct  ratio  of  the  weights  of  these  two  fluids,  and 
of  their  capacity  for  heat. 

The  capacity  of  the  steam  being  to  that  of  nitrogen 


4 1 2  On  the  Heat  developed  in  Combustion 

as  1.55  to  0.7036  (according  to  Crawford),  all  the  heat 
in  question  will  be  divided  so  that  the  steam  shall 
retain  the  part  of  it  represented  by  the  number  9.5832 
(=8.3333  X  I-SS)  '  an<^  the  nitrogen  will  receive  the 
other  part  of  it,  =  19.41  (being  the  product  of  27.587 
multiplied  by  0.7036). 

Now,  as  the  two  numbers  9.5832  and  19.41  are  bo.th 
in  the  proportion  of  i  to  2.0254,  it  is  evident  that  the 
temperature  will  be  the  same  which  we  should  have  if 
all  the  heat  in  question  was  equally  divided  between 
the  steam  which  would  result  from  the  combustion 
of  3.0254  pounds  of  hydrogen,  i.  e.  between  25.2113 
pounds  of  steam. 

And  as  we  have  seen  that  the  heat  manifested  in  the 
combustion  of  i  pound  of  hydrogen,  which  is  in  the 
8.3333  pounds  of  steam  which  are  the  products  of  this 
combustion,  is  sufficient  for  raising  the  temperature  of 
this  steam  to  that  of  8750°  F.,  it  is  evident  that  if  this 
same  quantity  of  heat  is  divided  among  25.2113  pounds 
of  steam,  the  temperature  of  this  steam  could  not  be 
higher  than  2891°  F. 

This  is,  therefore,  the  highest  temperature  which  we 
ought  to  find  in  the  midst  of  a  strong  fire  fed  by  the 
atmospheric  air  in  which  the  combustible  burned  is 
pure  hydrogen. 

As  this  temperature  is  much  lower  than  that  which 
we  can  excite  by  combustion,  even  without  employing 
pure  hydrogen  or  pure  oxygen,  the  result  of  this  calcu- 
lation furnishes  a  demonstrative  proof  that  the  capacity 
for  heat  of  steam,  or  rather  that  of  nitrogen,  is  diminished 
when  its  temperature  is  increased.  In  all  probability, 
the  capacities  of  both,  and  generally  of  all  elastic  fluids, 
are  diminished  when  their  temperature  is  increased. 


and  in  the  Condensation  of  Vapours.          413 

We  shall  now  see  what  is  the  highest  temperature 
which  it  would  be  possible  to  attain  by  burning  char- 
coal, and  by  blowing  the  fire  with  pure  oxygen  gas. 

According  to  Crawford,  I  pound  of  charcoal  gives 
heat  sufficient  in  its  combustion  to  raise  the  temperature 
of  57.608  pounds  of  water  180°  F.,  or  to  raise  the  tem- 
perature of  9369.44  pounds  of  water  i  degree. 

Now,  as  i  pound  of  charcoal  is  united  to  2.5714 
pounds  of  oxygen  in  burning,  and  forms  with  it  3.5714 
pounds  of  carbonic  acid,  the  heat  which  is  found  in 
3.5714  pounds  of  carbonic  acid  at  the  instant  of  its  forma- 
tion would  be  sufficient  to  raise  the  temperature  of 
9369.44  pounds  of  water  i  degree;  consequently  the 
heat  which  is  in  i  pound  of  this  acid  at  the  moment 
of  its  formation  would  be  sufficient  to  raise  the  tempera- 
ture of  3643.6  pounds  of  water  i  degree. 

Here  we  have  the  quantity  of  heat  which  exists  in  the 
carbonic  acid  at  the  instant  of  its  formation.  In  order 
to  know  what  is  the  intensity  which  it  would  indicate 
if  we  could  measure  it  at  this  moment  by  means  of  a 
thermometer,  it  would  be  necessary  to  know  precisely 
the  specific  heat  of  the  carbonic  acid.  If,  with  Crawford, 
we  take  it  at  1.0459  (tnat  of  water  being  taken  =  i), 
we  shall  have  3811°  F.  for  the  measure  of  the  intensity 
of  the  heat  which  exists  in  the  carbonic  acid  at  the 
moment  of  its  formation,  and  consequently  for  the 
intensity  of  the  greatest  fire  made  with  charcoal  (without 
mixture  of  hydrogen),  even  in  the  case  where  the  fire  is 
fed  by  -pure  oxygen. 

It  remains  to  determine  the  temperature  which  we 
might  hope  to  obtain  by  burning  charcoal  with  atmos- 
pheric air. 

As  we  have  found  that  the  temperature  of  the  3.5714 


414  On  the  Heat  developed  in  Combustion 

pounds  of  carbonic  acid,  which  are  the  product  of  the 
combustion  of  i  pound  of  charcoal,  is  that  of  3811°  F. 
at  the  moment  of  its  formation,  we  have  only  to  ascertain 
how  much  the  temperature  of  this  acid  ought  to  be 
diminished  by  the  mixture  of  the  nitrogen  which  must 
'necessarily  be  there  when  the  oxygen  employed  in  the 
combustion  of  the  charcoal  is  furnished  by  the  atmos- 
pheric air. 

As,  in  the  atmospheric  air,  every  pound  of  oxygen 
is  mixed  with  3.7619  pounds  of  nitrogen,  the  2.5714 
pounds  of  oxygen  employed  in  the  combustion  of  I 
pound  of  charcoal  ought  to  be  mixed  with  9.6735 
pounds  of  nitrogen  ;  consequently  all  the  heat  devel- 
oped in  the  combustion  of  i  pound  of  charcoal  will 
be  found  divided  between  3.5714  pounds  of  carbonic 
acid  and  9.6735  pounds  of  nitrogen. 

And  as  the  specific  heat  of  the  carbonic  acid  is  to  that 
of  nitrogen  as  1.0459  to  °'7°3^j tms  neat  w^  be  divided 
between  these  two  substances  in  the  proportion  of 
(3.5714  X  1.0459  =)  3-7354  to  (96735  X  0.7036=) 
6.8062,  which  is  in  the  proportion  of  i  to  6.8221  or  of 
3.5714  to  6.5075;  and  thence  we  may  conclude  that 
the  temperature  of  the  mixture  of  3.5714  pounds  of  car- 
bonic acid  and  of  9.6735  of  nitrogen  would  be  the  same 
as  if  we  had  mixed  with  the  3.5714  pounds  of  carbonic 
acid  6.5075  pounds  more  of  this  same  acid,  making  to- 
gether 10.0789  pounds  of  carbonic  acid. 

Now,  as  the  heat  developed  in  the  combustion  of  i 
pound  of  charcoal  was  sufficient  to  raise  the  temperature 
of  the  3.5714  pounds  of  carbonic  acid  coming  from  this 
combustion  to  that  of  3811°  F.,  this  same  quantity  of 
heat  ought  to  be  sufficient  to  raise  the  temperature  of 
10.0789  pounds  of  carbonic  acid  to  the  temperature 
of  1350°  F. 


and  in  the  Condensation  of  Vapours.          4 1 5 

This  is,  according  to  the  results  of  this  calculation, 
the  highest  temperature  which  we  ought  to  expect  to 
find  amid  the  strongest  charcoal  fire  fed  by  atmospheric 
air. 

But  we  are  very  certain  that  the  intensity  of  the  heat 
of  the  strongest  charcoal  fire  is  far  superior  to  the  above 
calculation  ;  consequently  we  are  authorized  to  conclude 
that  the  capacity  for  heat  of  the  carbonic  acid,  and  that 
of  nitrogen  gas,  are  much  diminished  when  these  elastic 
fluids  are  exposed  to  a  'very  high  temperature. 

If,  in  endeavouring  to  discover  the  limit  of  intensity 
of  a  charcoal  fire,  I  have  supposed  the  fire  to  be  'very 
large^  it  is  not  because  I  suppose  that  the  heat  developed 
in  combustion  is  more  intense  at  the  primitive  source  in  a 
large  than  in  a  small  fire ;  but  as  a  small  fire  is  always 
surrounded  by  bodies  relatively  very  cold,  such  as  the 
bars  of  the  grate,  etc.,  the  products  of  the  combustion 
(which  are  always  at  the  instant  of  their  formation  at  the 
same  temperature)  are  so  rapidly  cooled  when  the  fire  is 
small,  that  the  temperature  which  we  may  find  in  such  a 
fire  is  necessarily  lower  than  that  which  we  find  in  the 
midst  of  a  larger  fire,  where  a  greater  quantity  of  the 
same  kind  of  combustible  is  employed. 

When  a  large  charcoal  fire  is  well  lighted  up  in  a  close 
stove,  constructed  with  bricks  or  fire-stones,  all  the  inte- 
rior surfaces  become  excessively  hot,  and  the  heat  accu- 
mulates and  becomes  very  intense  throughout  the  whole 
'interior  of  the  stove,  so  that  iron  and  even  stones  are 
melted  in  it,  and  flow  like  liquids ;  but  when  the  fire- 
place is  small,  it  is  with  difficulty  that  it  can  be  heated 
so  much  as  to  make  the  sides  red-hot ;  and  if  the  fire- 
place be  very  small,  a  charcoal  fire  cannot  be  kept  up  at 
all,  even  with  continual  blowing.  We  may  truly  say 


41 6  On  the  Heat  developed  in  Combustion 

that  such  a  fire  dies  of  cold,  an  expression  which  with  as 
much  force  as  justice  describes  the  event  as  it  really 
happens. 

But  if  it  be  the  cold  communicated  by  the  surround- 
ing bodies  which  hinders  a  very  small  charcoal  fire  from 
burning,  could  we  not  make  it  burn  by  guarding  it  in  a 
proper  manner  against  the  cold  ? 

This  is  an  experiment  which  I  tried  six  years  ago  with 
the  greatest  success,  and  which  ended  in  my  causing  to 
be  made  small  portable  cooking-stoves  now  in  general 
use  in  Paris,  and  elsewhere  for  aught  I  know. 

By  surrounding  the  body  of  the  stove  with  two  strata 
of  enclosed  air,  the  cooling  of  the  fireplace  and  the  char- 
coal it  contains  is  hindered ;  and  in  this  way  the  char- 
coal burns  perfectly  well,  and  the  fire  is  so  well  kept  up 
that  it  obeys  a  small  register,  which  regulates  the  quan- 
tity of  air  admitted  into  the  body  of  the  stove. 

Some  judgment  may  be  formed  of  the  advantages 
which  ought  to  result  from  the  use  of  these  small  porta- 
ble furnaces  in  cooking,  etc.,  arising  from  the  saving  of 
time  and  combustibles,  when  we  are  informed  that  the 
combustion  may  be  regulated  without  any  difficulty,  so 
as  to  consume  the  charge  of  charcoal  in  20  minutes  with 
a  brisk  heat,  or  so  as  to  keep  up  a  moderate  fire  for 
three  hours. 

With  these  portable  cooking-stoves  it  is  indispensably 
necessary  to  use  kettles  or  saucepans  of  a  particular 
construction.  They  ought  to  be  suspended  by  their 
rims,  in  large  circles  of  wrought-iron  or  copper,  the  bet- 
ter to  keep  in  the  heat.  The  circle  of  a  saucepan  ought 
to  be  half  an  inch  more  in  breadth  than  the  saucepan  is 
in  depth. 

But  to  return  to  the  main  branch  cf  my  subject.      If 


and  in  the  Condensation  of  Vapours.          417 

the  present  state  of  our  knowledge  does  not  admit  of 
our  establishing  with  a  rigorous  precision  the  highest 
temperature  which  it  is  possible  to  excite  by  means  of 
the  combustion  of  inflammable  bodies,  the  calculation 
which  I  have  submitted  to  the  Class  may  nevertheless 
serve  to  guide  our  conjectures  on  this  interesting  sub- 
ject. They  will  at  all  events  show  what  is  wanting  to 
enable  us  duly  to  appreciate  the  subject. 

SECTION  X.  —  On  the  Quantity  of  Heat  developed  in  the 
Condensation  of  the  Vapour  of  Water. 

Having  filled  the  calorimeter  and  placed  it  on  its 
stand,  a  current  of  vapour  was  introduced  into  the 
worm  through  a  cork  placed  in  the  lower  aperture  of 
the  worm.  This  cork  having  been  perforated  with  a 
hole  two  lines  in  diameter,  in  the  direction  of  its  axis, 
a  small  cork  (two  lines  in  diameter  and  two  in  height) 
was  fitted  into  it,  and  four  other  holes  about  a  line  in 
diameter,  pierced  horizontally  through  the  sides  of  the 
large  cork  at  two  lines  below  its  upper  extremity,  and 
communicating  with  the  hole  two  lines  in  diameter  in 
the  axis  of  this  cork,  afforded  a  passage  to  the  vapour, 
to  admit  of  its  entering  by  four  small  channels  horizon- 
tally into  the  worm. 

As  the  apertures  of  these  small  channels  were  higher 
than  the  level  of  the  flat  bottom  of  the  worm,  the  water 
which  resulted  from  the  condensation  of  this  vapour 
did  not  prevent  the  vapour  from  continuing  to  flow 
through  these  passages. 

This  vapour  came  from  a  long-necked  matrass  contain- 
ing distilled  water,  which  was  put  on  a  portable  stove 
placed  in  a  chimney  at  some  distance  from  the  calorime- 

VOL.  ii.  27 


4 1 8          On  the  Heat  developed  in  Combustion 

ter ;  and  in  order  to  stop  all  direct  communication  of 
heat  between  the  stove  and  the  calorimeter,  the  former 
was  masked  by  plates,  and  the  tube  which  conducted 
the  vapour  to  the  calorimeter  was  well  covered  with 
flannel. 

The  cold  water  which  filled  the  calorimeter  was  of  a 
lower  temperature  than  that  of  the  chamber  by  6°  F., 
and  when  the  thermometer  of  the  calorimeter  announced 
an  augmentation  of  temperature  by  12°  F.,  an  end  was 
put  to  the  experiment. 

The  water  produced  by  the  condensation  of  the  va- 
pour in  the  worm  was  carefully  weighed;  and  from  its 
quantity,  as  well  as  from  the  heat  communicated  to  the 
calorimeter,  the  heat  developed  by  the  vapour  in  its  con- 
densation was  determined. 

As  a  small  part  of  the  heat  communicated  to  the 
calorimeter  proceeded  from  the  cooling  of  the  water 
condensed  in  the  worm,  after  the  vapour  had  been 
changed  into  water,  an  account  was  kept  of  this  heat. 
It  was  supposed  that  the  water  at  the  moment  of  con- 
densation was  at  the  temperature  of  212°  F.,  being  that 
of  boiling  water  ;  and  it  was  determined,  by  calculation, 
what  part  of  the  heat  communicated  to  the  calorimeter 
must  have  been  owing  to  this  boiling  water. 

In  making  this  calculation,  no  account  was  taken  of 
the  difference  in  the  capacity  of  water  for  heat  which 
depends  on  its  temperature  ;  this  is  but  imperfectly 
known,  and  besides,  the  correction  which  would  have 
been  the  result  could  not  but  have  been  very  small. 

The  following  are  the  details  and  results  of  two  ex- 
periments made  on  the  2ist  of  January,  1812. 


and  in  the  Condensation  of  Vapours.          419 


Dumber 
of  exp. 

Temper- 
ature of 
the 
room. 

State  of  the  calorimeter  (equal  in  capacity 
for  heat  to  2,781  grammes  of  water). 

Quantity  of 
vapour  con- 
densed into 
water  in  the 
worm. 

Result. 

Quantity   of  wa- 
ter which  maybe 
heated  1°  F.  with 
the  heat  devel- 

Temperature 
at  the  begin- 
ning of  the 

Temperature 
at  the  end  of 
the  experi- 

Elevation of 
its  tempera- 

experiment. 

ment. 

ture. 

densation  of  i  lb. 

'     of  vapour. 

Degr's. 

Degrees. 

Degrees. 

Degrees. 

Grammes. 

Ibs. 

I 

61 

55 

67\ 

in 

29.61 

1029.3 

2 

62} 

57} 

67i 

•°i 

24.4 

1052.3 

Mean  result                                                                                    1040.8 

By  expressing  the  mean  result  of  these  two  experi- 
ments in  the  way  employed  by  Mr.  Watt  and  others,  I 
shall  say  that  1040  degrees  of  heat  (Fahrenheit)  are 
liberated  in  the  condensation  of  steam,  and  that  con- 
sequently this  very  quantity  of  heat  is  employed  and 
rendered  latent  when  the  water,  already  at  the  tempera- 
ture of  boiling  water,  is  changed  into  steam. 

The  duration  of  each  of  these  two  experiments  was 
from  ten  to  eleven  minutes,  and  I  had  boiled  the  water 
some  time  in  the  matrass  (to  drive  out  the  air  which  it 
contained)  before  I  directed  the  steam  from  it  into  the 
worm  of  the  calorimeter. 

As  the  results  of  these  experiments  have  been  very 
uniform,  and  as  they  agree  very  well  with  the  later  ex- 
periments made  by  Mr.  Watt  with  a  view  to  determine 
the  same  question,  I  have  not  thought  it  necessary  to 
repeat  them. 

I  have,  besides,  been  very  much  occupied  with  the  fol- 
lowing branch  of  my  inquiries. 


SECTION  XI. —  Of  the  Quantity  of  Heat  developed  in  the 
Condensation  of  the  Vapour  of  Alcohol. 

As  chemists  are  not  agreed  as  to  the  state  of  the  ele- 
ments of  the  water  which  exist  in  alcohol,  I  thought 
that,  by  determining  with  precision  the  quantity  of  heat 


420          On  the  Heat  developed  in  Combustion 


which  is  developed,  we  should  be  better  able  to  form 
conjectures  as  to  the  state  of  the  water,  if  it  be  at  all 
times  found  in  this  inflammable  liquid. 

The  results  of  the  experiments  which  I  made  with 
alcohol  are  less  regular  than  those  of  the  experiments 
made  with  water,  as  might  have  been  expected  ;  but  they 
have  nevertheless  been  sufficiently  uniform  to  establish 
a  fact  which  will  be  regarded,  without  doubt,  as  very 
curious  and  important. 

As  the  vapour  which  is  extracted  from  spirit  of  wine 
when  boiled,  varies  a  little  with  the  intensity  of  the  fire 
used  in  boiling  it,  I  took  care  to  note  the  time  which 
was  taken  in  every  experiment,  in  order  to  be  able  to 
judge,  by  comparing  the  quantity  of  vapour  condensed 
with  the  time  employed  to  form  it,  of  the  intensity  of 
the  heat  employed  to  boil  the  liquid. 

In  the  following  table  we  shall  see  the  details  and 
results  of  five  experiments  made  on  the  same  day 
(January  21,  1812)  with  alcohol  of  different  degrees  of 
strength.  The  capacity  of  the  calorimeter  was  always 
equal  to  that  of  2781  grammes  of  water,  and  the  ther- 
mometer employed  was  that  of  Fahrenheit. 


3 

9 

r 

State  of  the  calor 

meter. 

ij 

Result. 

1 

1 

I 

9 

| 

B 

V 

1 

if 

l?^c 

1 

11 

I 

1 

Z 

a 

i 

-SJ 

HKi 

1 

1! 
P 

u 

IS. 

li 

1! 

1 

1 

v  £ 

Us' 

f  ^ll  i 

Jz; 

CO 

H      ' 

H 

s 

& 

§ 

Min. 

Uram. 

I 

85342 

7 

61° 

541° 

68i° 

1  44° 

69.86 

499.54 

2 

85342 

5 

61 

56 

66^ 

IOJ 

52.21 

476.83 

3 

84714 

8 

6oJ, 

55* 

^5i 

10 

48.82 

500.03 

4 

81763 

4i 

61 

56 

66-^ 

IO2 

56.6l 

479.92 

5 

85342 

6* 

64 

57 

7»i 

Hi 

7I-31 

499.65 

and  in  the  Condensation  of  Vapours.          42 1 

On  determining,  by  calculation,  the  quantity  of  water 
which  may  be  heated  one.  degree^  by  the  heat  developed 
in  the  combustion  of  one  pound  of  this  vapour,  I  took 
care  to  keep  an  account  of  the  difference  between  the 
capacity  of  water  for  heat  and  that  of  alcohol,  when  I 
determined  how  much  heat  should  have  been  communi- 
cated to  the  calorimeter  by  the  alcohol,  and  produced 
by  the  condensation  of  the  steam,  by  being  cooled  in  the 
worm. 

In  order  to  prove  the  state  of  the  elements  of  the 
water  which  exist  in  the  steam  of  alcohol,  it  must  be 
shown  how  much  water  these  elements  ought  to  form. 

We  shall  select  the  experiment  which  was  made  with 
alcohol  of  the  specific  gravity  of  81,763,  and  which  con- 
tained the  least  water.  The  quantity  of  steam  con- 
densed in  this  experiment  was  56.61  grammes. 

In  100  parts  of  this  alcohol  there  were 

91.79  parts  of  pure  alcohol  of  Lowitz,  and 
8.21  parts  of  water. 

Consequently  there  were  in  the  56.61  grammes  of 
alcohol  condensed  in  the  calorimeter, 

51.962  grammes  of  alcohol  of  Lowitz,  and 
4.648  grammes  of  water. 

Now,  as  M.  de  Saussure  has  shown  that  there  are  47 
parts  of  water  in  100  parts  of  alcohol  of  Lowitz,  there 
must  have  been  24.422  grammes  of  water  in  the  51.962 
grammes  of  alcohol  of  Lowitz,  which  were  condensed  in 
the  calorimeter. 

If  to  this  quantity  of  water  (  =  24.422  grammes)  we 
add  the  4.648  grammes  which  were  found  mixed  with 
51.962  grammes  of  alcohol  of  Lowitz,  in  order  to  com- 
pose the  56.61  grammes  of  alcohol  employed  in  the 


422  On  the  Heat  developed  in  Combustion 

experiment,  we  shall  have  29.07  grammes  of  water  which 
ought  to  have  existed  ready  formed  either  in  the  common 
state  of  water  or  in  some  other  state,  in  the  56.61  grammes 
of  alcohol  condensed  in  the  calorimeter. 

But  the  condensation  of  29.07  grammes  of  steam  into 
liquid  water  ought  to  have  of  themselves  furnished  more 
heat  than  we  had,  in  the  experiment  in  question,  in  the 
condensation  of  these  29.07  grammes  of  elements  of 
water  with  27.57  grammes  of  carbon  and  hydrogen, 
which  concur  with  these  elements  in  forming  the  steam 
of  the  alcohol  which  was  condensed. 

If  we  apply  a  similar  calculation  to  the  results  of  the 
experiments  made  with  alcohol  which  contained  more 
water,  the  result  of  the  inquiry  will  be  still  more  strik- 
ing. 

In  the  experiment  No.  5  the  alcohol  employed  was 
of  the  specific  gravity  of  85,342  ;  consequently  100  parts 
of  this  alcohol  were  composed  of 

77.88  parts  of  alcohol  of  Lowitz,  and 
22.12  water. 

And  in  the  experiment  71.31  grammes  of  vapour  of 
alcohol  were  condensed. 

There  were,  therefore,  in  these  71.31  grammes  of  con- 
densed alcohol, 

55.688  grammes  of  alcohol  of  Lowitz,  and 
15.622  grammes  of  water. 

In  the  55.688  grammes  of  alcohol  of  Lowitz  there 
were  26.102  grammes  of  water,  according  to  the  analysis 
of  M.  de  Saussure ;  and  this  last  quantity  of  water 
(  =  26.012  grammes),  added  to  the  quantity  found  above, 
viz.  15.622  grammes,  makes  41.727  grammes  of  water 
which  ought  to  have  existed,  either  as  steam  or  other- 


and  in  the  Condensation  of  Vapours.          423 

wise,  in  the  7 1.31  grammes  of  alcoholic  vapour  condensed 
in  the  calorimeter,  in  the  experiment  in  question. 

In  order  to  simplify  our  calculation,  and  to  render 
our  comparisons  more  striking,  we  shall  show  how  much 
pure  water,  in  vapour,  ought  to  have  been  sufficient  to 
furnish,  in  its  condensation,  the  same  quantity  of  heat 
which  was  furnished  by  the  condensation  of  71.31 
grammes  of  alcoholic  vapour,  in  the  experiment  in 
question. 

In  this  experiment  the  temperature  of  the  calorimeter 
was  raised  to  14}°  of  Fahrenheit. 

In  the  second  experiment,  made  with  the  steam  of 
pure  water,  the  temperature  of  the  same  calorimeter  was 
raised  io|°  of  Fahrenheit,  with  the  heat  developed  in 
the  condensation  of  24.4  grammes  of  this  vapour. 

Consequently  the  temperature' of  the  calorimeter  must 
have  been  elevated  to  14^°  of  Fahrenheit,  with  the  heat 
which  must  have  been  developed  in  the  condensation 
of  33-695  grammes  of  steam  from  pure  water. 

Now,  as  the  hydrogen  and  the  oxygen  forming  the  ele- 
ments of  41.727  grammes  of  water,  which  are  found  to 
form  constituent  parts  of  the  71.31  grammes  of  vapour 
of  alcohol  condensed  in  the  experiment  in  question,  only 
furnished  in  their  condensation  the  same  quantity  of 
heat  as  33-695  grammes  of  steam  of  pure  water  should 
have  furnished,  it  is  clearly  proved,  in  my  opinion,  that 
these  elements  are  not  so  united  as  to  form  water,  so 
long  as  they  concur  in  the  formation  of  alcohol. 

I  have  discovered  that  the  vapour  of  sulphuric  ether 
furnishes  about  one  half  less  of  heat  in  its  condensation 
than  that  of  alcohol,  and  consequently  one  fourth  only 
of  what  is  furnished  by  the  steam  of  water  of  equal 
weight ;  but,  having  been  interrupted  by  an  accident  in 


424       On  the  Heat  developed  in  Combustion,  etc. 

the  course  of  my  experiments  with  ether,  I  am  desirous 
of  finishing  them  before  I  publish  the  results. 

[The  first  three  sections  of  this  paper  are  printed  from  Nicholson's 
Journal,  Vol.  XXXII.  (1813),  pp.  105-125;  the  remainder  from 
Tilloch's  Philosophical  Magazine,  Vol.  XLI.  (1813),  pp.  439  —  444, 
and  Vol.  XLII.  pp.  296-307,  and  Vol.  XLIII.  (1814),  pp.  64-69. 
On  pages  392,  410,  and  412  there  are  several  numerical  errors  and  in- 
consistencies ;  but,  as  the  original  French  memoirs  are  not  accessible,  no 
attempt  has  been  made  to  reconcile  them.] 


ON    THE    CAPACITY    FOR    HEAT 


CALORIFIC  POWER  OF  VARIOUS  LIQUIDS. 

THIS  subject  is  of  rather  an  obscure  nature,  and  it 
has  been  so  little  examined,  that  it  will  be  useful 
to  begin  by  elucidating  it  as  well  as  I  can. 

Let  us  suppose  two  cylindrical  vessels,  with  very  thick 
sides,  made  of  lead  or  any  other  metal,  and  perfectly 
equal  in  size,  each  being  capable  of  containing  a  pint. 

These  two  vessels  being  at  the  freezing-point,  we 
shall  pour  into  the  one  a  pound  of  water  at  the  tem- 
perature of  96°  F.  (=  28J°  R.),  being  that  of  the 
blood,  and  into  the  other  a  pound  of  olive  oil  at 
the  same  temperature. 

Each  of  these  liquids  will  heat  the  cold  vessel  in 
which  it  is  placed,  the  vessel  in  its  turn  will  cool  the 
liquid,  and  both  the  liquid  and  the  vessel  will  latterly 
be  of  the  same  temperature. 

If  water  and  oil  of  olives  had  the  same  calorific  power, 
a  pound  of  water  at  the  temperature  of  96°  would  heat  its 
cold  vessel  precisely  as  much  and  not  more  than  a  pound 
of  oil  would  heat  its  vessel,  the  two  vessels  being  of 
the  same  weight  and  at  the  same  temperature  at  the 
commencement  of  the  experiment. 

But  experience  shows  that  water  heats  its  vessel  much 
more  than  oil  does ;  consequently  the  calorific  power  of 
water  is  greater  than  the  calorific  power  of  oil  of  olives, 


426  On  the  Capacity  for  Heat,  or 

when  the  quantities  of  these  two  liquids  are  estimated  by 
their  weight ;  and,  if  we  designate  the  calorific  power 
of  water  by  i,  the  calorific  power  of  oil  of  olives  will 
be  expressed  by  a  fraction  under  i. 

The  power  with  which  any  given  body,  solid  or 
liquid,  being  at  a  given  temperature,  resists  the  calorif- 
ic or  frigorific  action  of  bodies  warmer  or  colder  than 
itself,  is  in  proportion  to  its  calorific  power;  and  the 
greater  is  this  power,  the  longer  it  resists  these  actions 
of  surrounding  bodies. 

If,  under  equal  surfaces,  a  pound  of  water  and  a 
pound  of  oil  of  olives,  both  at  the  same  temperature 
(96°  F.),  are  placed  at  the  same  time  in  a  place  where 
the  temperature  is  lower  (that  of  freezing,  for  instance), 
the  oil  of  olives  will  be  cooled  much  more  rapidly  than 
the  water. 

If  it  be  in  a  warm  place  that  the  two  liquids  are 
exposed,  the  oil  of  olives  will  still  have  its  temperature 
most  rapidly  changed ;  it  will  be  more  heated  than  the 
water. 

In  two  cylindrical  glass  vessels,  of  equal  size  and  very 
thin,  place  equal  quantities  of  water,  and  at  the  same  tem- 
perature (96°  F.). 

A  piece  of  lead  weighing  a  pound,  and  a  piece  of  cop- 
per of  the  same  weight,  having  been  cooled  in  a  mixture 
of  pounded  ice  and  water,  remove  them  from  this  cold 
mixture  and  plunge  each  of  them  suddenly  into  one  of 
the  vessels  of  water. 

The  two  masses  of  water  will  be  cooled,  but  that 
which  contains  the  copper  most,  for  the  calorific  power 
of  copper  is  greater  than  the  calorific  power  of  lead. 

We  may  also  say  that  the  frigorific  power  of  copper  is 
greater  than  the  frigorific  power  of  lead,  and,  in  the  case 


Calorific  Power  of  various  Liquids.  427 

in  question,  the  expression,  perhaps,  will  be  most  suit- 
able. 

It  is  always  the  same  power;  it  is  that  by  means  of 
which  any  body  resists  the  action  of  surrounding  bodies, 
and  which  tends  to  change  its  temperature  either  by  in- 
crease or  diminution. 

Much  obscurity  has  been  introduced  into  the  science 
by  vague  ideas  being  attached  to  the  words  hot  and  cold; 
but  it  will  not  suit  my  purpose  to  enlarge  upon  this 
subject  at  present.  I  have  already  delivered  my  opinion 
in  a  former  paper. 

The  little  heat  which  I  discovered  in  the  condensation 
of  alcohol  having  induced  me  to  think  that  the  specific 
heat  of  this  liquid  had  not  been  accurately  determined, 
and  wishing  to  know  it  precisely,  in  order  to  enable  me 
to  finish  the  calculations  which  were  necessary  for  eluci- 
dating the  results  of  some  of  my  experiments,  I  con- 
structed a  small  and  very  simple  apparatus,  by  the  help 
of  which  I  could  easily,  and  as  I  presume  accurately, 
determine  it. 

This  apparatus  consists  of  a  small  bottle  of  a  particu- 
lar form,  constructed  of  thin  leaves  of  red  copper,  in- 
tended to  contain  the  liquid  which  is  to  be  the  subject  of 
the  experiment ;  and  a  small  cylindrical  vase,  also  con- 
structed of  thin  pieces  of  red  copper,  in  which  I  place 
water  at  a  certain  temperature.  Into  this  water  I  plunge 
the  bottle  of  copper  containing  the  liquid  which  is  the 
subject  of  the  experiment;  this  liquid  being  of  a  differ- 
ent temperature  from  that  of  the  water  in  the  outer  vase. 

As  the  capacity  of  the  vase  for  heat,  as  well  as  that 
of  the  bottle,  is  known,  I  determine,  by  a  very  simple 
calculation,  the  capacity  for  heat  of  the  liquid  contained 
in  the  bottle.  This  calculation,  which  is  well  known,  is 


428  On  the  Capacity  for  Heat,  or 

founded  in  the  changes  which  take  place  in  the  temper- 
ature of  liquids,  in  the  vase  and  in  the  bottle,  by  taking 
a  uniform  temperature,  when  the  bottle  is  immersed  in 
the  water  contained  in  the  vessel. 

In  order  that  this  equality  of  temperature  may  be 
speedily  brought  about,  the  form  of  the  bottle  is  such 
that  it  has  a  very  great  surface  relative  to  its  small 
capacity,  and  in  order  to  manage  it  without  touching  it, 
its  neck,  which  is  small,  is  closed  by  a  long  cork,  which 
serves  as  a  handle. 

In  order  to  diminish  as  much  as  possible  the  effect 
of  the  atmosphere  and  of  surrounding  bodies  upon  the 
apparatus,  while  the  experiment  is  going  on,  the  quan- 
tity of  water  in  the  vessel  is  regulated  so  as  to  keep  the 
bottle  wholly  submerged  in  the  liquid,  and  even  the 
upper  end  of  the  neck  covered,  when  the  bottle  is  im- 
mersed. The  vessel  which  contains  this  water  is  placed 
and  suspended  by  a  ring  of  cork  in  another  vessel  larger 
and  higher,  and  the  interval  between  the  two  is  filled 
with  eider-down. 

The  form  of  the  bottle  is  such  that  its  horizontal 
section  presents  the  figure  of  a  rectangular  cross.  Some 
idea  may  be  conceived  of  its  form  and  dimensionSj  if 
we  suppose  a  square  piece  of  stick,  each  facet  of  which 
is  four  lines  broad  by  four  inches  three  lines  in  length, 
upon  the  four  faces  of  which  we  have  fixed  four  sticks  of 
the  same  length  (i.  e.  four  inches  three  lines),  but  each 
of  them  being  four  lines  thick  by  eight  broad. 

The  four  sticks  last  described  will  exhibit  the  figure 
of  the  bottle ;  for  the  square  piece  of  stick  will  be  con- 
cealed by  them  from  our  view. 

The  neck  of  the  bottle  is  in  the  prolongation  of  its 
axis ;  it  is  four  lines  diameter  by  four  high  ;  it  ought  to 


Calorific  Power  of  various  Liquids.  429 

be  circular;  the  cork  should  be  an  inch  long,  and  the 
bottle  weigh  76.07  grammes  without  its  cork. 

The  cylindrical  vase  which  contains  the  water  is  two 
inches  diameter,  and  four  inches  nine  lines  high,  and  it 
weighs  74.65  grammes. 

The  exterior  vessel,  in  which  the  latter  is  suspended 
by  the  cork  ring,  is  five  inches  three  lines  high,  and 
three  inches  diameter,  so  that  the  sides  and  bottom  are 
everywhere  separated  by  an  interval  of  six  lines;  this  in- 
terval is  filled  with  eider-down,  as  already  mentioned. 

To  prevent  the  water  from  touching  the  eider-down, 
the  cork  ring  is  covered  with  a  thin  coating  of  mastic. 

In  order  to  ascertain  the  temperature  of  the  bottle, 
and  of  the  liquid  which  it  contains,  without  being 
obliged  to  plunge  a  thermometer  into  the  bottle,  which 
would  in  this  case  be  inconvenient,  I  employed  a  very 
simple  method. 

I  placed  a  large  bucket  filled  with  water  in  a  room 
with  a  northern  aspect.  I  allowed  it  to  assume  the 
temperature  of  the  room,  taking  care  to  shut  the  door 
and  windows  day  and  night.  I  placed  the  small  bottle 
on  a  stand  in  this  bucket,  keeping  the  upper  part  of  the 
cork  only  out  of  the  water.  As  the  bottle  is  small  and 
has  a  large  surface,  it  speedily  acquires  the  temperature 
of  the  bucket  of  water ;  but,  in  order  to  be  well  con- 
vinced that  the  bottle  and  the  liquid  which  it  contains 
have  acquired  the  temperature  in  question,  I  leave  the 
bottle  a  considerable  time  in  the  bucket,  frequently  half 
an  hour  and  sometimes  more. 

In  giving  a  detailed  account  of  an  experiment  made 
with  this  apparatus,  I  shall  have  an  opportunity  of  giv- 
ing clear  and  precise  ideas  of  the  different  parts  of  my 
apparatus,  and  of  the  particular  objects  which  they  are 
intended  to  attain. 


430  On  the  Capacity  for  Heat,  of 

Having  found  by  various  preliminary  experiments 
made  with  water  that  the  capacity  for  heat  of  the  cylin- 
drical vessel  with  that  of  the  thermometer  employed  to 
determine  the  temperature  of  the  water  which  it  con- 
tained, was  equal  to  that  of  24.3  grammes  of  water,  and 
that  the  specific  heat  of  the  bottle  of  copper  was  equal 
to  that  of  8.36  grammes  of  water,  I  made  the  following 
experiment  with  purified  linseed-oil. 

I  put  into  the  cylindrical  vessel  180  grammes  of 
water ;  the  temperature  of  the  room  was  59^°  F.  I 
filled  the  copper  bottle  with  the  above  oil,  and  corked  it. 
I  cooled  it  in  a  bucket  of  water  at  the  temperature 
of  44j°  F.  The  oil  in  the  bottle  weighed  82.55 
grammes. 

The  bottle,  having  had  time  to  acquire  the  tempera- 
ture of  44!°  F.,  was  withdrawn  from  the  bucket,  and 
placed  in  a  cylindrical  vessel  of  tinned  iron,  of  about 
four  inches  diameter  and  six  high,  filled  to  the  height 
of  four  inches  and  a  half  with  water  at  the  temperature 
of  44i°  F. 

The  bottle,  being  submerged  in  this  vessel  of  cold 
water,  was  carried  into  the  room  where  I  had  placed  the 
small  vessel  of  copper  belonging  to  the  apparatus;  it 
was  then  taken  out  of  the  cold  water,  and  plunged  into 
the  water  contained  in  the  small  cylindrical  vessel  of 
copper,  which  contained  180  grammes  of  water  at  the 
temperature  of  59^°  F. 

A  thermometer  having  a  cylindrical  reservoir  four 
inches  long,  which  was  placed  in  this  vessel  beside  the 
copper  bottle,  soon  fell,  and  in  three  or  four  minutes  it 
marked  56^-°  of  F.,  where  it  remained  a  long  time  sta- 
tionary, and  afterwards  began  to  ascend  slowly. 

The  capacities   for  heat  of  the  warm  bodies  which 


Calorific  Power  of  various  Liquids.  431 

were   cooled  in  this  experiment  were  equal  to  that  of 
204.3  grammes  of  water  ;  viz.,  — 

That  of  the  water  employed        .         .         .         .         180  grammes. 
That  of  the  vases  and  thermometer          .         .         .    24.3 


Total         .         .          .     204.3 
The  capacity  for  heat  of  the  bottle  containing  the  oil  was  equal  to 

that  of 8.36  grammes  of  water. 

And  to  this  we  must  add  the  cold  water  ad- 
hering to  the  bottle,  when  it  came  out  of  the 
cold  water,  and  was  plunged  into  the  water 
contained  in  the  copper  vessel.  I  found  by  a 
particular  experiment  that  this  quantity  of 
water  was  ......  1.04 

Total  ....       9.40 

Now,  as  the  temperature  of  the  warm  water  in  the 
cylindrical  vase  of  copper  was  that  of  59!°  before  the 
mixture,  and  56^°  after  the  communication  of  the  heat 
had  been  obtained,  it  is  evident  that  this  water  was 
cooled  2-f°.  But  if  we  multiply  the  number  of  grammes 
of  water  which  the  specific  heat  of  this  water  represents, 
and  that  of  the  vessel  (=  204.3  grammes),  by  the  number 
of  degrees  which  it  has  been  cooled  (2|)  we  shall  have 
a  product  which  will  express  the  number  of  grammes 
of  water  which  would  have  been  cooled  i°  F.  by  a 
loss  of  heat  equal  to  that  which  the  vessel  and  its  con- 
tents supported  in  this  experiment.  It  is  204.3  X  2.75 
=  561.84  grammes. 

We  shall  now  see  what  part  of  this  heat  was  com- 
municated to  the  bottle  and  to  the  small  portion  of 
cold  water  attached  to  it,  and  what  part  to  the  oil  con- 
tained in  the  bottle. 

As  the  temperature  of  the  bottle  and  its  contents  was 
44 £°  F.  before  the  mixture,  and  65^°  afterwards,  it  is 


43 2  On  the  Capacity  for  Heat,  or 

evident  that  the  bottle  had  acquired  \i\°  of  heat ;  conse- 
quently, if  we  multiply  9.4  (the  number  which  expresses 
the  sum  of  the  capacities  for  heat  of  the  bottle,  and  of 
the  cold  water  adhering  to  it)  by  12^  we  shall  have  a 
product  which  will  express  the  number  of  grammes  of 
water  which  would  have  been  heated  one  degree  by  the 
heat  communicated  during  the  experiment  to  the  bottle, 
and  to  the  small  portion  of  water  which  adhered  to  it. 

It  is  94 X  12.25=  111-15  grammes. 

If  from  the  heat  lost  by  the  vessel  and  the  warm 
water,  which  we  have  found  equal  to  that  which  is 
necessary   for  raising   the   temperature  of  561.84 
grammes  of  water  one  degree  of  F.,     .         .         .         561.84  grammes 
we   take   the  quantities    which   the  bottle  and   the 
water  adhering  to  the  bottle  have  received    .         .        115.15 

we  shall  have     .         .         .         '.-'.-        .         .         446.69  grammes 

of  water  heated  one  degree,  expressing  the  quantity  of 
heat  employed  for  raising  to  12-^°  F.  the  temperature 
of  the  82.55  gimmes  of  linseed  oil  which  were  put 
into  the  bottle. 

On  dividing  this  number  (446.69)  by  ii\,  we  shall 
see  how  many  grammes  of  water  would  have  been 
heated  one  degree  by  the  quantity  of  heat  in  question. 

It  is  therefore   _       °  —  36.464  grammes  of  water. 

By  the  results  of  this  calculation  we  find  that  the 
same  quantity  of  heat  which  is  necessary  to  raise  the 
temperature  of  36.464  grammes  of  water  12^  degrees 
of  Fahrenheit's  thermometer  is  sufficient  to  raise  the 
temperature  of  82.55  grammes  of  oil  the  same  number 
of  degrees. 

Consequently  the  capacity  of  water  for  heat  is  greater 
than  that  of  oil  of  linseed  in  the  proportion  of  82.55  to 


Calorific  Power  of  various  Liquids.  433 

36.464 ;  and  if  we  express  the  capacity  of  the  water  by 
«»//>',  as  is  usually  done,  the  capacity  of  the  above  oil 
ought  to  be  expressed  by  the  fraction  0.44172. 

These  details  must  no  doubt  appear  superfluous  to 
those  who  are  versed  in  the  higher  branches  of  knowl- 
edge, and  who  are  accustomed  to  express  the  most  com- 
plete relations  by  algebraical  signs  ;  but  it  must  be  rec- 
ollected that  the  subject  of  which  I  treat  is  familiar  to 
few,  and  that  it  is  necessary  to  explain  with  rigorous 
accuracy  the  principles  upon  which  the  method  em- 
ployed is  founded,  as  well  as  the  manner  of  using  the 
apparatus  which  I  recommend. 

On  repeating  twice  the  experiment  made  with  pure  linseed  oil  I 
had  as  a  result  in  one  of  these  experiments  a  capacity  for  heat  equal 

to o  4441 1 

and  in  the  other  equal  to     ......     0.47193 

If  to  these  two  results  we  add  that  of  the  first  ex- 
periment, equal  to  ......          0.44172 

we  shall  have  as  a  mean  result      ...  .      0.45192 

The  following  are  the  results  of  some  experiments 
made  with  other  liquids.  Olive  oil  furnished :  — 

Specific  heat  of  olive  oil. 

ist  experiment 0.45944 

2d  experiment         .......     0.43422 

3d  experiment     ....          ...         0.42183 

Mean  result     .         .         .     0.43849 

Three  experiments  made  with  naphtha  gave  the  fol- 
lowing results  :  — 

Specific  heat  of  naphtha. 

1st  experiment  ......         0.43408 

2d  experiment         .......     0.39234 

3d  experiment 0.41905 

Mean  result     .         .         .     0.41519 
VOL.  ii.  28 


434    On  the  Capacity  for  Heat  of  various  Liquids. 

Three  experiments  made  with  spirits  of  turpentine 
gave  the  following  results  :  — 

Specific  heat  of  turpentine. 

1st  experiment 0.29322 

zd  experiment 0.37031 

3d  experiment 0.34216 

Mean  result     .         .         .     0.33856 

Two  experiments  with  alcohol,  of  the  specific  gravity 
of  817,624,  gave  the  following  results :  — 

Specific  heat  of  alcohol. 

1st  experiment     .......         0.54924 

ad  experiment        ••-        §         *         .         .         .         .     0.55063 


Mean  result     .         .         .     0.54993 

Two  experiments  with  spirit  of  wine,  of  the  specific 
gravity  of  85,324,  gave  the  following  results:  — 

Specific  heat  of  spirit  of  wine. 

1st  experiment     .         .         .  . "     .  .         .         0.57840 

zd  experiment         .         .         .         •  '•'••         .     0.58317 

Mean  result      .  .     0.58078 

Two  experiments  with  sulphuric  ether,  of  the  specific 
gravity  of  72,880,  gave  as  results  :  — 

Specific  heat  of  sulphuric  ether. 

1st  experiment    .......         0.53711 

2d  experiment         .  '    .   . ' 0.54768 

Mean  result     ...      *     0.54329 

I  was  at  first  much  surprised  to  find  so  great  a  ca- 
pacity for  heat  in  sulphuric  ether,  but  my  astonishment 
was  diminished  when  I  recollected  that  this  liquid  can 
unite  with  alcohol  in  all  proportions  without  exhibiting 
any  symptoms  of  a  chemical  action  ;  for  this  reason, 
therefore,  we  ought  to  expect  to  find  the  same  capacity 
for  heat  in  both  liquids. 

[This  paper  is  printed  from  Tilloch's  Philosophical  Magazine,  XLIII.  (1814),  pp. 
212-218.] 


INQUIRIES 

RELATIVE  TO  THE  STRUCTURE  OF  WOOD, 

The  specific  Gravity  of  its  solid  Parts,  and  the  Quantity 
of  Liquids  and  elastic  Fluids  contained  in  it  under 
various  Circumstances  ;  t/ie  Quantity  of  Charcoal  to 
be  obtained  from  it;  and  the  Quantity  of  Heat  pro- 
duced by  its  Combustion* 

SINCE  the  days  of  Grew  and  Malpighi,  there  have 
been  but  few  regular  inquiries  into  the  structure 
of  wood.  The  science  of  botany  has,  indeed,  taken 
an  excursive  range  ;  and  the  indefatigable  zeal  of  mod- 
ern naturalists,  who  have  travelled  over  all  the  known 
world,  has  made  us  acquainted  with  an  astonishing 
number  of  plants,  unknown  before  in  Europe,  and 
therefore  called  new,  by  which  our  gardens  and  apart- 
ments are  embellished  with  a  profusion  of  gay  flowers  ; 
but  still  the  knowledge  of  the  vegetable  economy  is 
scarcely  at  all  advanced.  The  circulation  of  the  sap  in 
plants  is  still  a  subject  of  dispute,  and  the  causes  of  its 
ascension  are  very  imperfectly  known.  The  specific  grav- 
ity of  the  solid  parts  which  form  the  wood  of  plants  is 
unascertained,  and,  by  consequence,  the  proportions  of 
solids,  of  liquids,  and  of  elastic  fluids ;  the  component 
parts  of  a  plant,  with  the  variations  to  which  they  are 
subject  in  different  seasons,  are  matters  of  which  we  are 
still  ignorant. 


436     Inquiries  relative  to  the  Structure  of  Wood. 

It  is,  indeed,  known,  that  the  wood  of  a  tree  remains 
and  preserves  its  primitive  form  after  it  has  been  con- 
verted into  charcoal ;  but  no  one  has  explained  this 
extraordinary  phenomenon,  very  little  attention  having 
been  paid  to  it. 

An  earthen  vessel  becomes  hard  and  brittle  in  the 
potter's  furnace  ;  the  vessel  shrinks  during  the  operation 
of  baking,  but  it  undergoes  no  alteration  of  shape. 
This  phenomenon  is  easily  accounted  for;  the  water, 
which  distended  the  particles  of  the  clay,  kept  them  at 
a  distance  from  each  other,  and  rendered  the  mass  soft 
and  flexible,  having  been  expelled  by  the  power  of  the 
heat,  the  several  particles  contract  themselves  together, 
and  form  a  hard  brittle  body,  though  the  clay  remains 
the  same  before  and  after  the  operation. 

Is  it  not  possible  that  wood  is  converted  into  char- 
coal by  a  similar  process  ?  For  either  the  charcoal  is 
already  formed  in  the  wood,  or,  the  wood  being  decom- 
posed, the  charcoal  is  formed  of  its  elements  or  a  part 
of  them.  But  is  it  not  evidently  impossible  that  the 
elements  of  a  solid  body  should  be  so  totally  deranged 
as  to  separate  them  entirely  from  each  other  without 
destroying  the  form  or  figure  of  the  body  ? 

In  the  sequel  of  this  paper  it  will  be  shown  that  the 
specific  gravity  of  the  solid  parts  of  any  kind  of  wood 
is  very  nearly  the  same  as  that  of  the  charcoal  obtained 
from  it,  —  a  circumstance  that  gives  a  great  degree  of 
probability  to  the  hypothesis  that  the  two  substances 
are  identically  the  same. 

But  I  do  not  mean  to  amuse  the  Class  with  a  detail  of 
my  own  conjectures  ;  it  is  to  my  experiments  and  their  re- 
sults that  I  now  claim  the  honour  of  calling  its  attention. 

I    was  by  accident  first  induced  to  enter  upon  this 


Inquiries  relative  to  the  Structure  of  Wood.    437 

examination  and  inquiry  into  the  structure  of  wood. 
In  the  course  of  a  long  series  of  researches  upon  heat, 
I  wished  to  determine  the  quantities  of  that  element 
produced  by  the  combustion  of  different  kinds  of  wood; 
but  I  had  scarcely  begun  the  inquiry  when  I  found  that, 
in  order  to  procure  satisfactory  results  to  my  experi- 
ments, it  was  indispensably  necessary  to  obtain  a  better 
knowledge  of  wood  itself;  and  therefore  I  immediately 
devoted  myself  to  the  study. 

My  first  aim  was  to  determine  the  specific  gravity  of 
the  solid  parts  which  compose  the  fabric  of  the  wood, 
in  order  afterwards  to  determine  the  quantities  of  sap 
or  water  contained  in  wood  under  various  circumstances. 

Having  found  that  very  thin  shavings  filled  with  sap, 
or  even  with  water,  could  be  thoroughly  dried  in  less 
than  an  hour,  without  injury  to  the  wood,  in  a  stove 
kept  at  a  higher  temperature  than  that  of  boiling  water, 
or  at  about  500°  of  Fahrenheit's  scale  (=  260°  French), 
I  determined  on  using  shavings  of  this  description  in 
my  experiments. 

SECTION  I.  —  Of  the  specific  Gravity  of  the  solid  Parts 
of  Wood. 

I  began  with  the  wood  of  the  lime-tree,  of  which  the 
texture  is  very  fine  and  regular.  From  a  small  board, 
five  inches  long  and  half  an  inch  thick,  very  dry,  I  took 
a  quantity  of  thin  shavings  with  a  very  sharp  plane. 
These  were  exposed  for  eight  days  in  the  month  ot 
January  upon  a  table  in  a  large  room  not  otherwise 
occupied,  in  order  that  they  might  attract  from  the 
atmosphere  all  that  moisture  which,  as  an  hygrometric 
body,  they  were  capable  of  imbibing.  The  temperature 
of  the  room  was  about  46°  F. 


438     Inquiries  relative  to  the  Structure  of  Wood. 

Ten  grammes  (154.5  grains)  of  those  shavings,  laid 
on  a  china  plate,  were  placed  in  a  large  stove  made  of 
sheet-iron,  and  there  exposed  to  a  regular  heat  of  about 
245°  F.  for  two  hours,  in  the  course  of  which  time  they 
were  frequently  taken  out  and  weighed  in  order  to  observe 
the  progress  of  their  desiccation.  When  they  ceased  to 
lose  weight,  the  operation  was  stopped ;  when  perfectly 
dried,  their  weight  was  8.121  grammes. 

By  previous  trials  with  my  apparatus,  I  had  learned 
that  if  the  stove  was  too  much  heated  the  shavings 
became  discoloured,  which  is  always  indicated  by  the 
emission  of  a  particular  odour,  very  readily  to  be  per- 
ceived ;  but,  by  a  careful  regulation  of  the  fire,  this 
accident  may  be  avoided  and  the  shavings  be  thoroughly 
dried  without  injury,  or  even  subjecting  them  to  any 
sensible  alteration. 

I  concluded  that  they  had  not  undergone  any  change, 
because,  upon  again  exposing  them  to  the  atmosphere, 
they  regained  the  same  weight  which  they  had,  under 
similar  circumstances,  prior  to  their  being  dried  in  the 
stove. 

Being  thus  possessed  of  the  weight  of  my  shavings, 
as  well  under  exposure  to  the  air  as  in  a  dried  state, 
which  latter  I  could  not  but  look  upon  as  being  perfect, 
it  only  remained  to  ascertain  their  weight  in  water  when 
all  their  vessels  and  pores  were  completely  filled  with 
that  liquid,  to  enable  me  to  determine  the  specific  grav- 
ity of  the  solid  parts  of  this  wood,  which  was  accom- 
plished without  difficulty  by  the  following  process  :  — 

A  cylindrical  copper  vessel,  10  inches  in  diameter  and 
as  many  deep,  was  filled  with  water  from  the  Seine, 
previously  well  filtered,  and,  being  set  upon  a  common 
chafing-dish,  was  made  to  boil  for  some  time,  to  expel 


Inquiries  relative  to  the  Structure  of  Wood.    439 

the  air  contained  in  the  water.  The  shavings  were  then 
thrown  into  the  boiling  water,  and  kept  in  that  state  for 
an  hour.  The  water  was  not  long  in  filling  the  vessels 
and  pores  of  the  shavings,  from  which  it  dislodged  the 
air  contained  in  them  ;  so  that  the  wood,  specifically 
heavier  than  the  water,  was  precipitated  to  the  bottom 
of  the  ves.se!,  and  there  remained. 

When  the  vessel  was  removed  from  the  chafing-dish, 
the  water  was  suffered  to  cool  to  the  temperature  of  60° 
F.,  and  then,  plunging  in  both  hands,  I  placed  (under  the 
water)  all  the  shavings  in  a  cylindrical  glass  vase,  whose 
weight  I  had  previously  ascertained,  which  was  sus- 
pended in  the  water  by  a  silken  cord,  fastened  at  its 
other  extremity  to  the  arm  of  an  accurate  hydrostatic 
balance. 

On  weighing  the  shavings  in  the  glass  case  thus  im- 
mersed, I  found  their  weight  equal  to  2.651  grammes. 

As  the  shavings,  while  dry,  weighed  8.121  grammes 
in  the  air,  and  2.651  grammes  in  the  water,  they  must 
have  lost  5.47  grammes  of  their  weight  in  the  latter ; 
consequently  they  must  have  displaced  5.47  grammes  of 
water;  and  the  specific  gravity  of  the  solid  parts  of  this 
wood  must  be  to  that  of  the  water  at  the  temperature 
of  60°  F.  as  8.1 21  to  5.47,  or  as  14,846  to  10,000. 

It  may  perhaps  excite  some  surprise  that  the  solid 
parts  of  so  light  a  wood  as  that  of  the  lime-tree  should 
be  heavier,  by  nearly  one  half,  than  water,  taken  in 
equal  bulks.  But  this  surprise  will,  without  doubt,  be 
increased  when  I  declare  that  the  specific  gravities  of  the 
solid  parts  of  all  kinds  of  wood  are  so  nearly  alike  as 
almost  to  induce  a  belief  that  there  is  the  same  identity 
in  the  ligneous  substance  of  all  sorts  of  wood  as  in  the 
osseous  substance  of  all  species  of  animals. 


440     Inquiries  relative  to  the  Structure  of  Wood. 


I  procured,  from  a  joiner's  workshop,  dried  wood 
of  the  eight  following  species ;  viz.,  poplar,  lime,  birch, 
fir,  maple,  beech,  elm,  and  oak  ;  and  had  them  cut  into 
small  boards,  5  inches  in  length  and  6  inches  broad, 
from  each  of  which  I  planed  off  some  thin  shavings, 
and  exposed  them  to  the  air  for  eight  days,  in  the 
month  of  January,  in  a  large  room,  where  the  tempera- 
ture, which  varied  but  little,  was  about  40°  to  45°  F. 

When  these  shavings  had  acquired  their  ordinary  de- 
gree of  dryness  under  existing  circumstances,  10  grammes 
of  each  sort  were  weighed  off,  and,  being  laid  separately 
in  china  plates,  were  thoroughly  dried  in  the  stove. 

On  being  taken  out  of  the  stove,  they  were  again 
weighed,  and  then  thrown  into  boiling  water,  to  ex- 
pel the  air  from  their  pores  and  to  moisten  them  thor- 
oughly. When  they  had  boiled  for  an  hour,  they  were 
suffered  to  remain  in  the  liquor  till  it  was  sufficiently 
cool ;  and  after  they  had  been  weighed  in  the  water, 
the  specific  gravity  of  their  solids  was  calculated  in  the 
usual  way. 

The  following  table  gives  the  details  and  results  of 
this  inquiry  :  — 


Species  of 
wood. 

Weight. 

Specific  gravity 
of  the  solid  parts 
of  the  wood. 

Weight  of 
a  cubic  inch  of 
the  solid  parts 
of  the  wood. 

Exposed 
to  the  air  in 
a  room  in 

Thoroughly 
dried  in  a 
stove. 

In  the  water 
at  60°  F. 

Grammes. 

Grammes. 

Grammes. 

Grammes. 

Poplar 

10 

8.045 

2.629 

14854 

29.45 

Lime 

10 

8.  121 

2.651 

14846 

29.40 

Birch 

10 

8.062 

2.632 

14848 

29.44 

Fir 

IO 

8.247 

2.60  1 

14621 

28.96 

Maple 

10 

8.137 

2.563 

14599 

28.93 

Beech 

10 

8.144 

2.832 

15284 

3°-3° 

Elm 

10 

8.180 

2-793 

15186 

30.1  1 

Oak 

10 

8.336       |         2.905 

15344 

30.42 

Water     10000              '9-83 

Inquiries  relative  to  'the  Structure  of  Wood.    441 

The  specific  weight  of  the  solid  matter  which  com- 
poses the  fabric  of  these  woods  is  so  nearly  alike  in 
them  all,  that  the  small  variations  to  be  observed  in  the 
different  experiments  may  perhaps  be  accounted  for 
otherwise  than  by  supposing  the  ligneous  substance  to 
be  essentially  different  in  the  several  species. 

The  charcoal  obtained  from  the  various  kinds  of 
wood,  if  carefully  prepared,  has  no  sensible  difference; 
and  all  the  seerwoods  give  nearly  the  same  chemical 
results  when  treated  in  the  same  manner.  Hence,  with- 
out doubt,  we  have  good  reason  to  suspect  that  the 
ligneous  substance  of  all  woods  is  identical.  But  with- 
out stopping  to  discuss  this  question  at  present,  I  shall 
endeavour  to  elucidate  another,  no  less  interesting,  and 
which  yields  results  more  satisfactory. 

SECTION  II.  — Of  the  Quantities  of  Sap  and  Air  discovered 
in  Trees  and  in  Seerwoods. 

Grew  and  Malpighi  discovered  in  plants  certain  ves- 
sels which  they  suspected  to  be  destined  for  the  recep- 
tion of  air;  and  many  physiologists  have  supposed  that 
the  air  found  shut  up  in  the  vessels  of  plants  (if  it 
be  really  confined  there)  would  necessarily  cause  a  re- 
action upon  the  neighbouring  vessels,  with  an  elastic 
force  as  variable  as  the  temperature  to  which  this  elastic 
fluid  is  exposed,  and  might  probably  contribute  to  the 
circulation  of  the  sap. 

It  would,  doubtless,  be  an  interesting  question  to  de- 
termine precisely  the  quantity  of  air  contained  in  plants 
in  different  seasons  and  under  various  circumstances. 
By  examining  the  variations  to  which  this  quantity  of 
air  is  subjected,  and  combining  them  with  other  simul- 


442     Inquiries  relative  to  the  Structure  of  Wood. 

taneous  phenomena,  we  might  hope  to  make  some  dis- 
covery which  may  assist  us  a  little  to  elucidate  the  pro- 
found obscurity  that  at  present  conceals  this  part  of  the 
vegetable  economy. 

The  specific  gravity  of  the  solid  parts  of  a  plant  being 
known,  it  becomes  very  easy  to  determine  in  every  case 
the  quantity  of  air  contained  in  its  vessels  and  pores. 

The  following  example  will  render  this  position  per- 
fectly clear. 

An  oak  in  complete  health,  in  a  growing  state,  was 
cut  down  on  the  6th  of  September,  1812.  A  cylindrical 
piece,  6  inches  long  and  rather  more  than  an  inch  in 
diameter,  taken  from  the  middle  of  the  trunk  of  this 
young  tree,  3  feet  above  the  earth,  weighed,  when  full 
of  sap,  181.57  grammes. 

Upon  plunging  this  piece  of  wood  into  a  cylindrical 
vessel  about  I J  inch  in  diameter  and  6\  inches  in  height, 
filled  with  water  at  the  temperature  of  62°  F.,  it  displaced 
188.57  grammes  of  the  water;*  whence  I  conclude 
with  certainty,  that  this  piece  of  oak,  filled  with  sap, 
possessed  a  bulk  equal  to  9.5093  cubic  inches,  that  its 

*  In  order  to  determine  and  keep  an  account  of  the  quantity  of  water  remaining  on 
the  surface  of  this  piece  of  wood  at  the  instant  of  withdrawing  it  from  the  vessel,  it 
was  weighed  when  taken  out,  whilst  still  quite  wet.  As  its  weight  had  been  taken 
previously  to  the  operation,  the  augmentation  it  had  acquired  from  the  water  was  ascer- 
tained to  a  nicety. 

The  vessel  when  empty  weighed  188.22  grammes,  and  when  filled  with  water  at 
the  temperature  of  60°  F.,  474.9  grammes  ;  so  that  it  contained  286.68  grammes  of 
water.  When  the  piece  of  wood  was  plunged  into  the  water,  a  small  glass  plate, 
about  two  inches  in  diameter  and  two  lines  in  thickness,  ground  with  emery  to  fit  it 
to  the  edges  of  the  vessel,  so  as  to  close  it  hermetically,  was  laid  upon  its  mouth,  to 
shut  up  the  piece  of  wood  with  the  water  still  remaining  in  the  vessel,  whilst  its  out- 
side was  wiped  with  a  dry  cloth. 

When  the  exterior  of  the  vessel  had  been  thoroughly  dried,  the  glass  cover  was 
carefully  removed,  and  the  piece  of  wood  withdrawn  ;  the  vessel  was  then  weighed 
again  with  its  remaining  contents  of  water  ;  and  from  its  weight  the  quantity  of  water 
displaced  by  the  wood  was  calculated. 


Inquiries  relative  to  the  Structure  of  Wood.    443 

specific  gravity  was  96,515,  and,  consequently,  that  a 
cubic  inch  of  it  weighed  19.134  grammes. 

When  the  piece  of  wood  had  been  reduced  to  the 
shape  of  a  small  board,  about  half  an  inch  in  thickness, 
I  took  from  it  forty  very  thin  shavings  weighing  19.9 
grammes,  but  when  thoroughly  dried  in  the  stove,  at 
a  temperature  of  262°  F.,  they  weighed  only  12.45 
grammes. 

From  this  experiment,  it  is  evident  that  the  wood  in 
question,  being  full  of  sap,  was  composed  of  12.45 
ligneous  parts,  and  7.45  parts  of  water,  or  of  sap,  whose 
specific  gravity  is  nearly  the  same  as  that  of  water. 

Now,  as  one  cubic  inch  of  this  wood  weighed  19.134 
grammes,  it  is  very  certain  that  it  was  composed  of 
11.971  grammes  of  ligneous  parts,  which  were  conse- 
quently solids,  and  of  7.163  grammes  of  sap. 

But  we  have  already  seen,  from  the  results  of  the 
experiments  detailed  in  the  former  part  of  this  memoir,* 
that  a  cubic  inch  of  the  solid  parts  of  the  wood  of  the 
oak  weighs  30.42  grammes  :  — 

Consequently  the  11.971  grammes  of  solid  parts 
found  in  one  cubic  inch  of  this  wood,  when  the 
tree  was  alive,  could  have  no  greater  bulk 
than 0-39353  cubic  inch. 

As  one  cubic  inch  of  water  weighs  19.83 
grammes,  the  7.163  grammes  of  sap  found  in 
the  cubic  inch  of  this  wood  must  have  occu- 
pied a  bulk  equal  to  .....  0.36122 

Consequently  a  cubic  inch  of  the  wood  in  ques- 
tion contained  a  quantity  of  air  whose  bulk 
was  equal  to 0.24525 

Making  together     ....          l.ooooo 

*  See  the  table,  page  440. 


444     Inquiries  relative  to  the  Structure  of  Wood. 

We  conclude  from  these  results,  that  a  young  oak,  in 
a  growing  state,  at  the  beginning  of  September,  when 
the  wood  appears  to  be  diffused  with  sap,  contains,  nev- 
ertheless, about  a  fourth  of  its  bulk  of  air,  and  that  its 
solid  ligneous  parts  do  not  make  quite  -fa  of  its  bulk. 
But  we  shall  presently  see  that  the  lighter  woods  contain 
still  less  of  ligneous  parts,  and  more  of  air,  than  the  oak. 

A  young  Italian  poplar,  3  inches  in  diameter,  meas- 
ured at  2  feet  above  the  earth,  was  cut  down  on  the 
6th  of  September,  while  the  tree  appeared  to  be  in  a 
growing  state.  The  specific  gravity  of  a  piece  taken 
from  the  middle  of  the  trunk  was  found  to  be  57,946; 
consequently  a  cubic  inch  of  this  wood  weighed  11.49 
grammes. 

From  a  piece  of  this  wood,  apparently  full  of  sap, 
forty  thin  shavings  were  taken,  6  inches  in  length'  and 
half  an  inch  broad.  The  wood  from  which  these  shav- 
ings were  planed  weighed  12.37  grammes;  and  the 
shavings,  when  thoroughly  dried  in  the  stove,  weighed 
7.5  grammes.* 

We  hence  conclude  that  a  cubic  inch  of  this  wood,  in 
its  original  state,  while  the  tree  was  still  alive,  contained 
7.1531  grammes  of  ligneous  parts  which  formed  the 
fabric  of  the  wood,  and  4.3369  grammes  of  sap,  differ- 
ing in  its  specific  gravity  little  or  nothing  from  common 
water. 

*  As  the  heat  excited  by  the  plane  in  taking  off  these  shavings  was  sufficient  to 
evaporate  a  very  sensible  quantity  of  sap  belonging  to  the  wood  from  which  they  were 
cut,  the  shavings  became  perceptibly  dry  during  the  operation  ;  for  I  found  that  forty 
thin  shavings  sometimes  lost  more  than  one  gramme  (about  —  of  their  weight) 
in  less  than  a  minute.  In  order  to  obtain  their  true  weight,  whilst  they  still  remained 
part  of  the  wood,  I  adopted  the  precaution  of  weighing  the  piece  of  wood  both  the 
moment  before  and  the  moment  after  the  operation  of  planing.  The  difference  in 
the  weight  of  the  wood,  under  these  two  circumstances,  indicates  the  weight  neces- 
sary to  be  given  to  the  shavings,  and  which  is  here  always  attributed  to  them. 


Inquiries  relative  to  the  Structure  of  Wood.    445 

As  one  cubic  inch  of  the  solid  parts  of  this  kind 
of  wood  weighs  29.45  grammes,*  the  7.1531 
grammes  of  ligneous  parts  found  in  a  cubic 
inch  of  the  trunk  of  the  living  tree,  in  Sep- 
tember, could  only  have  occupied  the  space  of  0.24289  cubic  inch. 

And  the  4.3369  grammes  of  sap,  contained  in  it, 

only 0.21880 

Consequently,   in   one   cubic  inch  of  this  wood 

there  was  a  bulk  of  air  equal  to      .         .         .     0.53831 

Total I. ooooo 

The  difference  between  the  structure  of  the  oak  and 
of  the  poplar  becomes  very  conspicuous  on  making  a 
comparison,  according  to  the  subjoined  method,  between 
the  constituent  parts  of  these  two  kinds  of  wood,  both 
in  a  growing  state. 

Thus,  a  cubic  inch  of  wood  is  composed  of:  — 

Ligneous  parts.  Sap.  Air. 

The  oak       .         .         .     0.39353         0.36122         0.24525 
The  poplar        .         .         0.24289         0.21880         0.53831 

This  striking  difference  in  the  proportions  of  the 
ligneous  substance,  of  sap,  and  of  air,  discovered  in  these 
two  species,  sufficiently  explain  the  difference  observable 
in  their  weight  and  hardness.  This  inquiry  may  prob- 
ably lead  to  other  discoveries  of  more  general  utility  in 
the  study  of  the  vegetable  economy. 


SECTION  III.  —  Of  the  relative  Quantities  of  Sap  and  Air 
found  in  the  same  Tree,  in  Winter  and  in  Summer ;  and 
in  different  Portions  of  the  same  Tree,  at  the  same  Time. 

The  following  experiments  were  undertaken  with  a 
view  to  discover  the  difference  between  the  quantities  of 

*  See  the  table,  page  440. 


446     Inquiries  relative  to  the  Structure  of  Wood. 

sap  and  air  found  in  the  wood  composing  the  trunk  of 
a  large  tree,  in  winter  and  in  summer. 

On  the  2oth  of  January,  1812,  I  had  a  lime-tree  felled 
of  about  twenty-five  or  thirty  years'  growth,  which  had 
stood  among  several  others  of  the  same  age  in  my  gar- 
den at  Auteuil.  On  taking  a  piece  of  wood  from  the 
middle  of  the  trunk,  at  about  3  feet  above  the  ground, 
it  appeared  to  be  filled  and  even  drowned  in  sap.  Its 
specific  gravity  was  76,617  ;  consequently,  one  cubic 
inch  of  the  wood  weighed  15.788  grammes. 

Having  planed  off  10  grammes  of  thin  shavings  from 
this  piece,  and  dried  them  thoroughly  in  the  stove,  I 
found  their  weight  reduced  4.72  grammes. 

Thus  in  possession  of  the  specific  gravity  of  the  solid 
part  of  this  wood,  it  was  easy  to  determine,  with  the  aid 
of  these  data,  the  constituent  parts  of  a  cubic  inch, 
which  were  as  follows :  — 

Ligneous  parts         ....         0.25353  cubic  inch. 

Sap 0.44549 

Air .         0.30098 


On  the  8th  of  September,  in  the  same  year  (1812),  I 
had  a  piece  of  wood  (=  5.84  cubic  inches)  cut  from  the 
trunk  of  another  lime,  of  equal  age  with  the  former 
(from  25  to  30  years),  at  the  height  of  3  feet  above  the 
earth.  This  tree  was  in  a  growing  state,  and  the  piece 
taken  from  it,  after  it  had  been  trimmed  by  the  joiner, 
weighed  87.8  grammes,  and  displaced  115.8  grammes  of 
water,  at  the  temperature  of  62°  F. ;  consequently,  its 
specific  gravity  was  75,820.  In  the  month  of  January 
the  specific  gravity  of  this  same  species  of  wood  had 
been  found  to  be  79,617. 


Inquiries  relative  to  the  Structure  of  Wood.     447 

From  the  piece  of  wood  taken  from  the  tree  on  the 
8th  of  September,  I  had  14.19  grammes  of  thin  shav- 
ings planed  off,  which,  after  they  had  been  thoroughly 
dried  in  the  stove,  weighed  only  7.35  grammes.  Hence 
we  have,  as  the  constituent  parts  of  a  cubic  inch  of  this 
wood :  — 

Ligneous  parts 0.26489  cubic  inch. 

Sap 0.36546 

Air 0.36965 

1. 00000 

From  the  results  of  these  two  experiments,  we  may 
conclude  that  the  body  of  the  tree  contains  more  sap  in 
the  winter  than  in  summer,  and  more  air  in  summer 
than  in  winter.  But  the  following  experiments  demon- 
strate the  sap  to  be  very  disproportionately  distributed 
in  the  several  parts  of  the  same  tree,  at  the  same  season. 

On  the  8th  of  September,  I  had  a  branch,  about  3 
inches  in  diameter,  cut  from  the  lime  just  spoken  of, 
and  which  issued  from  the  trunk  at  the  height  of  10  feet 
above  the  surface  of  the  earth.  From  the  lower  end  of 
this  branch  I  took  a  piece  of  wood,  and  subjected  it 
to  the  investigation  requisite  to  ascertain  its  constituent 
parts. 

Its  specific  gravity  was  70,201.  The  same  day  I  found 
the  specific  gravity  of  a  piece  of  the  trunk  of  the  same 
tree  to  be  75,820. 

Surprising  as  this  difference  appeared,  my  astonish- 
ment was  still  more  excited,  on  finding  that  a  piece  of 
wood  of  three  years'  growth,  cut  from  the  upper  end  of 
the  same  branch,  where  it  was  but  one  inch  in  diameter, 
had  a  specific  gravity  of  85,240. 

There  was,  therefore,  much  more  sap  and  less  air  in 


448     Inquiries  relative  to  the  Structure  of  Wood. 

the  wood  of  the  upper  extremity  of  the  branch  than  in 
the  lower,  which  was  nearer  to  the  body  of  the  tree. 

I  afterwards  examined  the  young  shoots  of  the  current 
year,  in  the  same  tree,  as  well  as  in  several  other  species 
of  wood,  and  uniformly  found  that  the  specific  gravity 
of  the  young  wood,  that  is  to  say,  of  the  current  year, 
is  always  considerably  greater  than  that  of  the  same 
species  of  wood  when  grown  older.  Doubtlessly,  be- 
cause it  contains  more  sap  and  less  air  than  the  old 
wood. 

In  the  management  of  experiments  for  determining 
the  specific  gravity  of  wood  of  the  current  year,  it  is  in- 
dispensably necessary  to  take  an  account  of  the  space 
occupied  by  the  pith,  without  which  precaution  we 
shall  be  led  to  false  conclusions. 

I  found  the  specific  gravity  of  the  oak  of  the  current 
year  to  be  116,530;  that  of  the  elm  110,540.  Young 
shoots  of  these  trees,  deprived  of  their  bark  and  pith, 
descend  rapidly  on  being  thrown  into  water ;  whilst 
species  of  the  same  tree,  more  advanced  in  age,  swim 
on  the  surface,  even  when  the  wood  is  green,  and  more 
full  of  sap. 

This  fact  is  worthy  the  attention  of  persons  occupied 
in  the  study  of  vegetable  physiology. 

I  was  next  curious  to  examine  the  root  of  the  lime 
from  which  I  had  already  had  one  piece  of  wood  from 
the  trunk,  and  two  pieces  from  one. of  its  branches. 
With  this  view,  on  the  8th  of  September,  1812,  I  caused 
one  of  its  roots,  of  about  2  inches  diameter,  to  be 
taken  up,  and  cut  from  it  a  piece  weighing  93.25 
grammes,  which  displaced  115.8  grammes  of  water.  Its 
specific  gravity  was  80,527,  and,  consequently,  greater 
than  that  of  the  wood  extracted  from  the  trunk  of  the 


Inquiries  relative  to  the  Structure  of  Wood.     449 

same  tree,  but  less  than  that  cut  from  the  upper  end  of 
one  of  its  branches.  20.48  grammes  of  thin  shavings, 
from  this  piece  of  the  root  of  the  lime,  weighed  only 
10.85  grammes  after  being  thoroughly  dried  in  the 
stove. 

From  these  data,  I  determined  the   constituent  parts 
of  a  cubic  inch  of  the  root  thus :  — 

Ligneous  parts    .....     0.28775  cubic  inch. 

Sap 0.37358 

Air 0.33867 


The  constituent  parts  of  a  cubic  inch  of  the  body  of 
the  same  tree  were,  as  we  have  shown  :  — 

Ligneous  parts 0.26489  cubic  inch. 

Sap 0.36546 

Air 0.36965 


The  constituent  parts  of  a  cubic  inch  of  the  wood  of 
the  same  tree,  taken  the  same  day  from  the  lower  ex- 
tremity of  a  branch,  were :  — 

Ligneous  parts 0.25713  cubic  inch. 

Sap 0.27513 

Air 0.46774 


Lastly,  the  constituent  parts  of  a  cubic  inch  of  the 
wcod,  taken  near  the  upper  extremity  of  the  same  branch, 
wee :  — 

Ligneous  parts 0.25388  cubic  inch. 

>ap         .         .         .         ..-.-..         0.47599 
Vir 0.27013 

1 .00000 
vo,   a.  29 


450     Inquiries  relative  to  the  Structure  of  Wood. 


For  the  more  easy  comparison  of  the  results  of  these 
four  experiments  upon  the  wood  of  the  lime-tree,  made 
on  the  same  day,  with  different  portions  of  the  same  tree, 
I  have  collected  them  together  in  the  following  table. 


A  cubic  inch  of  wood  was 
composed  of 

Ligneous 
parts. 

Sap. 

Air. 

The  root        .... 
The  trunk           .... 
The  lower  end  of  a  branch 
The  upper  end  of        "       . 
Wood  taken  from  the  trunk  of  a  ~\ 
lime-tree  of  the  same  age,  on  > 
the  20th  of  Jan.            .          .       ) 

0.28775 
0.26489 
0.25713 
0.25388 

°-25353 

0-37358 
0.36546 
0.27513 
0.47599 

0.44549 

0.33867 
0.36965 
0.46774 
0.27013 

0.30098 

Being  desirous  to  ascertain  whether  a  difference  con- 
siderable enough  to  be  valued  existed  between  the  wood 
of  the  heart,  or  core,  and  the  sap-wood  found  between 
the  rind  and  the  body  of  the  same  tree,  I  took,  on  the 
nth  of  September,  an  elm  fagot,  5  inches  in  diameter, 
lopped  from  a  large  tree,  which  had  been  felled  on  the 
2oth  of  the  preceding  April,  and  had  two  cylindrical 
pieces,  each  6  inches  in  length,  cut  out  of  it.  The 
thickest  of  these  taken  from  the  core  weighed  I9I.O5/ 
grammes,  and  displaced  194.45  grammes  of  water;  thtf 
other,  consisting  of  the  sap-wood,  weighed  93.6' 
grammes,  and  displaced  111.45  grammes  of  water. 

The  specific  gravity  of  the  core  was,  therefore,  98,251; 
that  of  the  sap-wood,  81,764.  But  as  the  fagot  hd 
lain  exposed  to  all  the  summer  rains,  the  wood  was  ar 
from  being  dry.  I  was,  however,  much  surprised  at  ds- 
covering  that  the  core  of  the  wood  was  more  char/ed 
with  sap  or  water  than  that  of  the  same  kind  of  w-od 
when  in  a  growing  state,  —  a  fact  which  induces  a  us- 
picion  that  the  sap  in  trees  is  not  enclosed  in  vesels 
or  tubes  apparently  impervious  to  that  liquid. 


Inquiries  relative  to  the  Structure  of  Wood.    451 

To  obtain  a  better  knowledge  of  the  wood  in  ques- 
tion, I  planed  off  forty  shavings,  6  inches  in  length  and 
half  an  inch  in  breadth,  from  a  small  board  cut  from  the 
core  ;  with  an  equal  number  of  shavings,  of  similar  di- 
mensions, from  another  board  cut  from  the  sap-wood. 

The  forty  shavings  from  the  core,  taken  just  as  they 
were  planed  off,  weighed  16.37  grammes,  and  10.53 
grammes  after  they  had  been  thoroughly  dried  in  the 
stove. 

The  forty  shavings  of  sap-wood  weighed  1 6.97  grammes 
before  they  were  dried,  and  11.99  grammes  afterwards. 

Thus  possessed  of  the  specific  gravity  of  the  solid 
parts  of  this  kind  of  wood,  it  only  remained  to  deter- 
mine, from  these  data,  the  constituent  parts  of  an  inch 
of  the  wood,  which  was  readily  performed,  as  fol- 
lows :  — 

Ligneous  parts.  Sap.  Air. 

In  the  core  of  the  elm  .         .     0.41622         0.35055         0.23323 

In  the  sap-wood        .         .          .         0.38934         0.23994         °-37°72 

It  appears,  from  the  results  of  these  experiments,  that 
the  sap-wood  of  the  elm  contains  rather  more  ligneous 
parts  in  its  timber  than  the  core  of  the  same  tree ;  and 
that  it  contains  much  less  sap  and  more  air.  But  as 
the  tree  had  been  felled  nearly  five  months  before  it 
became  the  subject  of  investigation,  it  is  very  possible 
that  the  sap-wood  had  become  much  drier  than  the  core 
of  the  tree. 

I  had  purposed  to  repeat  these  experiments  upon 
wood  in  a  growing  state  and  upon  seerwood ;  but  the 
interference  of  other  occupations  has  prevented  a  con- 
tinuance of  the  inquiry.  It  cannot,  however,  but  lead 
to  results  curious  in  themselves  ;  and  I  therefore  recom- 
mend it  to  the  notice  of  all  students  in  vegetable  econ- 


452     Inquiries  relative  to  the  Structure  of  Wood. 

omy,  as  well  as  to  those  who  love  that  noble  science,  and 
feel  a  gratification  in  being  able  to  remove  the  veil  under 
which  the  mysterious  operations  of  nature  are  concealed. 
The  particular  object  which  I  had  in  view  in  explor- 
ing the  structure  of  wood  has  led  me  by  a  way  by  no 
means  likely  to  be  fertile  in  interesting  discoveries ;  but 
I  have  begun  the  work,  and  feel  myself  bound  to  com- 
plete it,  in  preference  to  every  other  consideration. 
These  fascinating  researches,  I  am  aware,  have  already 
carried  me  too  far,  and  I  must  now  resign  them  into 
the  hands  of  others,  in  order  to  fulfil  my  engagements. 
This  I  do  most  cheerfully,  and  it  will  give  me  the  great- 
est pleasure  to  behold  a  field,  too  long  neglected,  once 
more  broken  up. 

SECTION  IV.  —  Of  the  Quantities  of  Water  contained  in 
Woods  considered  as  dry,  or  Seerwoods. 

Wood  is  a  hygrometric  substance,  and,  when  exposed 
to  the  atmospheric  air,  always  imbibes  a  visible  quantity 
of  water,  varying,  however,  with  the  temperature  and 
humidity  of  the  air. 

If  the  moisture  in  the  wood  were  confined  in  vessels 
so  constructed  as  to  be  totally  impervious  to  water, 
the  fabric  of  the  wood  would  be  uniformly  the  same, 
with  the  exception  only  of  the  variations  caused  in  its 
dimensions  by  change  of  temperature,  in  which  case  it 
would  be  very  easy  to  determine  the  quantity  of  water 
contained  in  the  wood,  when  the  specific  gravity  of  its 
solid  parts  was  known.  But,  as  the  bulk  of  all  woods 
is  considerably  diminished  in  drying,  the  experiment  is 
rendered  rather  prolix,  though  by  no  means  difficult, 
and  its  results  are  clear  and  satisfactory. 


Inquiries  relative  to  the  Structure  of  Wood.    453 

A  few  examples  will  suffice  to  point  out  the  method 
to  be  pursued. 

The  composition  of  the  oak,  in  a  growing  state,  at 
the  beginning  of  September,  has  been  already  given.  In 
order  to  ascertain  the  change  which  this  wood  under- 
goes by  the  process  of  drying,  I  made  the  following 
experiment. 

From  a  fagot  of  oak,  5^  inches  in  diameter,  which, 
covered  with  its  bark,  had  been  exposed  to  dry  in  the 
open  air  for  eighteen  months,  I  took  a  piece  of  rather 
more  than  an  inch  square  and  6  inches  in  length;  it  was 
good  firewood,  and  seemed  very  dry. 

This  piece,  after  being  trimmed  by  the  joiner,  weighed 
126.2  grammes,  and  displaced  157.05  grammes  of  water; 
its  specific  gravity  was  consequently  80,357,  and  a  cubic 
inch  weighed  15.939  grammes. 

Forty-three  shavings  of  this  wood,  6  inches  long 
and  half  an  inch  broad,  weighed  17.9  grammes  ;  but 
when  thoroughly  dried  in  the  stove,  they  were  reduced 
to  13.7  grammes.  They  were  therefore,  prior  to  being 
put  into  the  stove,  composed  of  13.7  grammes  of  solid 
parts  —  that  is  to  say,  of  dry  or  seerwood  —  and  4.2 
grammes  of  water. 

The  results  of  this  experiment  indicate  that  100  kilo- 
grammes of  this  excellent  firewood  contained  76  kilo- 
grammes of  seerwood  and  24  of  water;  which  is, 
probably,  the  ordinary  state  of  the  best  firewood  sold  in 
the  timber-yards  of  Paris,  and  all  other  places. 

Were  the  wood  to  be  kept  for  several  years  in  a  dry 
place,  secured  from  the  rain,  it  is  possible  that  it  might 
become  dry  to  such  a  degree  as  to  contain  only  about  12 
per  cent  of  water,  and  88  of  seerwood.  But  it  will 
appear  in  the  sequel  that  wood  of  any  kind,  exposed  to 


454     Inquiries  /-dative  to  the  Structure  of  Wood. 


the  atmosphere,  could  never  become  more  dry,  on 
account  of  its  hygrometric  quality,  which  it  constantly 
preserves. 

The  following  are  the  constituent  parts  of  a  cubic 
inch  of  firewood  employed  in  this  experiment :  — 


Ligneous  parts,  or  seerwood 

Sap,  or  water 

Air 


0.40166  cubic  inch. 
.     0.18982 
0.40852 


Thus  we  are  enabled  clearly  to  demonstrate  the  differ- 
ence between  the  oak  in  a  growing  state,  and  the  same 
kind  of  wood  after  it  has  been  felled  and  dried  in  the 
air,  secured  from  the  rain,  for  eighteen  months  :  — 


Jn  a  cubic  inch  of  oak,  in  a  grow-  1 

Q-39353 

!  0.36122 

0.24525 

In  a  cubic  inch  of  the  same  kind  ~\ 

1 

of    wood,    after    it    had    been  > 

0.40  1  66 

i  0.18982 

0.40852 

felled  and  dried  for  18  months  ) 

| 

Dry  wood,     i       Water. 


By  comparing  the  relative  quantities  of  seerwood 
contained  in  a  piece  of  timber  while  in  a  growing  state, 
and  in  the  same  timber  after  it  has  been  dried,  we  may 
ascertain  how  much  its  fabric  has  shrunk  by  desicca- 
tion. 

It  appears  from  these  experiments,  that  the  oak  sold 
in  the  timber-yards  of  Paris  for  firewood  contains 
rather  more  than  one  half  of  the  sap  which  it  formerly 
had  in  a  growing  state. 

I  have  made  several  similar  experiments  upon  other 
species  of  wood ;  but  their  results  are  better  calculated 
for  exhibition  in  a  table  than  for  circumstantial  detail. 


Inquiries  relative  to  the  Structtire  of  Wood.    455 

SECTION  V.  —  Of  the  Quantities  of  Water  attracted  from  the 
Atmosphere  by  Woods  of  various  Species ',  after  being  per- 
fectly dried. 

It  has  been  long  known  that  charcoal  imbibes  the 
humidity  of  the  atmosphere  with  considerable  eager- 
ness ;  but  I  have  discovered  that  dry  wood  attracts  it 
with  still  greater  avidity.  The  following  are  the  details 
and  results  of  a  series  of  experiments  made  last  winter, 
with  a  view  to  elucidate  this  subject. 

Having  procured  thin  shavings,  about  5  inches  long 
and  half  an  inch  broad,  of  nine  different  species  of  the 
woods  of  our  climate,  in  order  more  certainly  to  re- 
duce them  to  an  equal  degree  of  dryness,  I  began  my 
experiment  by  boiling  them  for  two  hours  in  water,  that 
they  might  be  thoroughly  impregnated  with  that  ele- 
ment. 

I  then  dried  them  well  in  a  stove,  in  which  they  were 
kept  during  24  hours,  exposed  to  a  temperature  higher 
than  that  of  boiling  water,  at  about  250°  of  Fahrenheit's 
scale. 

On  taking  them  out  of  the  stove,  they  were  carefully 
weighed,  being  still  hot ;  they  were  then  suffered  to  re- 
main in  the  open  air  for  24  hours,  in  a  large  room, 
whose  temperature  was  uniformly  during  the  day  and 
night  at  about  45°  to  46°  F.  This  was  on  the  ist  of 
February,  1812. 

The  weight  of  the  shavings,  on  being  removed  from 
the  stove  thoroughly  dried,  and  after  having  been  ex- 
posed to  the  air  of  the  large  room,  was  as  follows  :  — 


456     Inquiries  relative  to  the  Structure  of  Wcod. 


Wei 

?ht. 

Species  of  wood 

On  being 
withdrawn  from 
the  stove. 

After  exposure 
for  24  hours,  in 

temperature  of 
V  F. 

Italian  poplar      ...... 
Lime-tree,  seasoned,  and  fit  for  the  joiner's  use 
"          green  wood           .... 
Beech    
Birch          

Grammes. 
3-58 
5.28 

5-39 

7.02 

4-  4-1 

Grammes. 

445 
6.40 

6.47 

8.62 

c.  4.7 

Fir         
Elm  
Oak       
Maple         

5.41 
5.87 
6.46 

4.76 

6.56 
7.16 

7-93 
5.85 

Hence  it  appears  that  100  parts  of  the  wood,  after  24 
hours'  exposure  in  the  large  room,  were  composed  of  dry 
wood  and  water  in  the  following  proportions  :  — 


loo  parts  of 

Poplar      . 
Lime-tree,  seasoned 

"          green 
Beech  . 
Birch 
Fir       . 
Elm 
Oak     . 
Maple      . 


Seerwood. 
80.55 
82.50 

83-3I 
8144 
80.62 
82.4 

81.80 
83.36 
81-37 


Water. 

'9-55 
17.50 
16.69 
18.56 
19.38 

7-53 
17.20 
16.64 
18.63 


I  suffered  all  these  woods  to  remain  in  the  large 
room  during  eight  days,  but  their  weight  was  very  little 
augmented  ;  and  as  often  as  the  temperature  of  the  air 
of  the  room  was  raised  above  46°  F.  they  lost  weight. 
So  that  the  above  may  be  considered  as  their  habitual 
state  of  dryness  during  the  winter,  in  our  climate. 

To  ascertain  the  quantity  of  moisture  habitually  re- 
tained by  these  woods  in  the  summer,  I  made  the  fol- 
lowing experiments. 

Thin  shavings  of  the  species  of  woods  below,  half  an 
inch  broad,  were  thoroughly  dried  in  the  stove,  and  then 


Inquiries  relative  to  the  Structure  of  Wood.    457 


exposed  for  24  hours  in  a  room  with  a  northern  aspect, 
whose  temperature  was  tolerably  uniform  at  62°  F.  The 
following  are  the  results  :  — 


Weight. 

At  the 

were  found 

Species  of  wood. 

Wlian    A~   . 

accustomed 
state  of 

When  dry. 

humidity  in 

the  air  at 

Seerwood. 

Water. 

62°  F. 

Grammes. 

Grammes. 

Parts 

Parts 

Elm,  the  core 

IO-53 

11.55 

9I.l85 

8.815 

"      the  sap-wood 

11.99 

I3-IS 

91.197 

8.803 

Oak,  seasoned  and  fit  for 

the  joiner's  use    . 

13.70 

15.05 

91.030 

8.970 

Oak  felled  6th  Sept.  . 

12.45 

13.70 

90.667 

9-333 

Lime,  seasoned 

7.27 

7.80 

93.205 

6.795 

"       when  growing  . 

6.75 

7-30 

92.466 

7-534 

"       the  root 

9.96 

10.80 

92.222 

7.778 

Elm,  seasoned     . 

9.25 

10.80 

9I-I33 

8.867 

Italian  poplar 

7.50 

8.00 

93-75° 

6.250 

With  a  view  to  ascertain  the  habitual  state  of  the 
dryness  of  woods  in  autumn,  I  carefully  preserved  these 
same  shavings  till  the  3d  of  November,  in  a  northern 
chamber,  not  inhabited  ;  at  which  period  its  tempera- 
ture had  stood  for  several  days  at  52°  F.,  with  little 
variation.  I  then  weighed  the  shavings,  and  from  their 
weight  calculated  the  quantity  of  water  contained  in 
them. 

The  following  table,  containing  the  results  of  all 
these  experiments,  displays,  in  a  familiar  and  satisfactory 
manner,  the  customary  state  of  the  woods,  in  different 
seasons,  in  our  climate. 


Species  of  wood. 

ioo  parts  in  weight  of  wood,  cut  into  thin  shavings  and 
exposed  to  the  air,  contained  water 

In  summer, 
at  a  temperature  of 
6/  F. 

In  autumn, 
at  a  temperature  of 

S£F. 

In  winter, 
at  a  temperature  of 
45°F. 

Poplar    .         . 
Lime  . 
Oak         ... 
Elm    . 

Parts. 
6.25 

7.78 
8.97 

8.86 

Parts. 

»•!$ 

11.74 
12.46 

I  1.  12 

Parts. 

'9-55 

17.50 
16.64 
17.20 

45 8     Inquiries  relative  to  the  Structure  of  Wood. 

From  a  comparison  of  these  results  it  appears  that 
these  woods,  when  exposed  to  the  air  at  a  temperature 
of  45°  F.,  contain  twice  the  quantity  of  water  that  they 
do  when  the  temperature  of  the  air  is  at  60°  F.  But  it 
is  necessary  that  the  wood  be  cut  into  very  thin  shav- 
ings, to  enable  it  to  become  suddenly  in  equilibria  with 
the  air,  conformably  to  its  quality  of  a  hygrometric 
body ;  otherwise  the  state  of  the  air  may  change,  and 
that  very  frequently,  before  its  humidity  or  dryness  can 
have  had  sufficient  opportunity  to  produce  all  its  effect 
upon  the  wood. 

To  discover  what  is  termed  the  medium  dryness  of  any 
species  of  wood,  in  our  climate,  it  is  requisite  that  we 
be  acquainted  with  the  quantity  of  water  contained  in 
wood  every  day  of  the  year,  and  even  in  every  hour  and 
every  minute,  which  is  obviously  impossible  ;  but  there 
is  another  method  to  be  pursued  in  this  inquiry,  much 
less  laborious  and  which  will  lead  to  results  as  satisfac- 
tory as  the  nature  of  the  subject  will  admit. 

As  a  very  large  piece  of  wood,  a  large  beam  for  in- 
stance, dries  so  very  gradually  in  the  air  as  not  to  attain 
a  state  of  perfect  dryness  in  less  than  50  or  60  years,  it 
is  sufficient  to  examine  the  interior  of  such  a  beam,  after 
having  been  sheltered  for  80  or  100  years  from  the  rain, 
to  discover  the  state  of  such  part  of  the  wood  as  may 
still  be  considered  sound. 

In  pulling  down  old  houses,  we  meet  with  beams 
proper  for  the  present  inquiry. 

An  old  castle  in  my  neighbourhood  being  pulled 
down,  I  had  an  opportunity  of  examining  the  interior 
of  a  large  oaken  beam,  which  had,  without  doubt,  been 
there  more  than  150  years,  and  as  it  formed  part  of  the 
timbers  of  the  edifice,  had  been  secured  from  the  rains. 


Inquiries  relative  to  the  Structure  of  Wood.     459 

A  piece  of  this  wood  in  a  high  state  of  preservation, 
after  it  had  been  planed  by  the  workman,  was  accurately 
weighed,  and  then  plunged  into  water,  to  ascertain  its 
specific  gravity.  It  weighed  75.05  grammes,  and  dis- 
placed no  grammes  of  water,  at  the  temperature  of 
61°  F.  ;  its  specific  gravity,  therefore,  was  68,227,  and  a 
cubic  inch  weighed  13.53  grammes. 

Forty  shavings  of  the  wood  weighed  11.4  grammes, 
which  were  reduced  to  10.2  grammes  when  they  had 
been  thoroughly  dried  in  the  stove. 

Hence  we  may  conclude  that  a  cubic  inch  of  this  old 
wood  was  composed  of 

Ligneous  parts  .....     0.39794  cubic  inch. 

Water 0.07186 

Air 0.53020 


We  may  also  conclude  from  these  results,  that  the 
wood  of  the  centre  of  a  large  oaken  post,  though  kept 
for  ages  out  of  the  reach  of  the  rain,  can  never  contain, 
in  our  climate,  less  than  10  per  cent  of  its  weight  in 
water;  and  that  a  cubic  inch  of  such  wood  contains 
more  than  half  a  cubic  inch  of  air. 

The  yearly  medium  temperature  at  Paris  is  about  54]-° 
F.  ;  now,  as  we  have  just  seen  that  the  habitual  state  of 
dryness  in  woods  at  the  temperature  of  52°  F.  is  such 
as  to  give  about  n  per  cent  of  water  for  100  parts  of 
wood,  we  must  not  be  surprised  at  finding  10  per  cent 
of  water  in  the  interior  of  a  large  beam,  after  it  had 
been  sheltered  from  the  rain  during  150  years.  . 

To  ascertain  whether  the  property  of  wood  to  attract 
moisture  from  the  atmosphere  was  augmented  or  dimin- 
ished by  the  beginning  of  carbonization,  I  made  the  fol- 
lowing experiments. 


460     Inquiries  relative  to  the  Structure  of  Wood, 

Fourteen  grammes  of  ash-shavings,  after  being  highly 
dried  on  a  marble  slab  over  a  chafing-dish,  were  exposed 
to  the  air,  in  the  month  of  February,  in  a  large  room 
whose  temperature  was  about  20°  F.,  and  in  15  hours 
they  had  gained  1.65  grammes  in  weight. 

Fourteen  grammes  of  the  same  sort  of  shavings,  hav- 
ing been  first  scorched  in  the  stove  till  they  had  assumed 
a  brown  color,  were  at  the  same  time  dried  over  the 
chafing-dish,  and  exposed  with  the  others  to  the  cold  air 
for  the  same  length  of  time  ;  but  they  gained  in  weight 
only  i.oi  grammes,  while  those  which  had  not  been 
scorched,  as  already  stated,  had  gained  1.65  grammes. 

Fourteen  grammes  of  the  shavings  of  lime-wood,  in 
their  natural  state,  and  fourteen  grammes  of  the  same 
kind  of  shavings,  after  they  had  been  violently  scorched 
in  the  stove,  were  dried  together  over  the  chafing-dish, 
and  then  exposed  in  the  open  air,  at  the  temperature  of 
40°  F.  for  15  hours.  The  shavings  in  their  natural 
state  gained  1.33  grammes  in  weight ;  while  those  that 
had  been  scorched  gained  0.7  grammes. 

A  similar  experiment,  upon  shavings  of  the  cherry- 
tree,  some  in  their  natural  state,  and  others  scorched, 
was  productive  of  the  same  result. 

Whence  we  conclude  that  wood  in  its  natural  state 
attracts  the  moisture  of  the  air  more  copiously  than  it 
does  after  having  been  subjected  to  the  first  degree  of 
carbonization. 

From  similar  experiments  upon  wood  and  charcoal,  I 
find  that  dry  wood  attracts  humidity  more  powerfully 
than  dry  charcoal. 

It  would  be  worth  ascertaining,  whether  wood  is  not 
also  more  powerfully  attractive  of  gas  than  charcoal  ; 
but  as  I  have  not  time  to  enter  upon  this  particular 


Inquiries  relative  to  the  Structure  of  Wood.     46 1 

inquiry,  I  can  only  recommend  it  to  those  whose  inclina- 
tions may  lead  that  way.  Leaving,  therefore,  this  subject 
untouched,  I  must,  without  any  further  circumerration, 
pursue  the  original  object  I  had  in  view  in  these  disqui- 
sitions upon  wood,  namely,  to  endeavour  to  become 
acquainted  with  those  inflammable  substances  which  burn 
on  setting  fire  to  a  piece,  of  wood  under  a  calorimeter. 

SECTION  VI.  —  Of  the  Quantities  of  Charcoal  to  be  obtained 
from  different  Kinds  of  Wood. 

Having  discovered  that  pieces  of  wood,  more  or  less 
thick,  may  be  perfectly  carbonized  in  glass  vases  with 
thin  tops,  closely  covered,  and  exposed  for  two  or  three 
days  to  a  moderate  heat  in  a  stove,  I  adopted  this 
method  in  all  my  experiments  on  the  carbonization  of 
wood. 

The  glass  vases  which  I  make  use  of  are  what  the 
chemists  call  proofs,  with  feet :  they  are  small  cylindrical 
vessels,  about  i^  inch  in  diameter  and  6  inches  in  height; 
the  covers  consist  of  glass  plates  about  2  inches  in  diam- 
eter and  from  2  to  3  lines  in  thickness,  neatly  ground 
with  very  fine  emery,  well  diluted  with  water,  on  a  large 
glass  slab  ;  and,  the  edges  of  the  vases  being  ground  with 
the  same  exactness,  they  become  hermetically  closed  by 
the  covers,  so  as  to  preclude  every  access  of  the  air,  es- 
pecially if  the  edges  of  the  vases  and  the  whole  surface 
of  the  covers  be  well  rubbed  with  black-lead. 

The  elastic  fluids,  in  escaping  from  the  interior  of  the 
vases,  occasionally  raise  the  cover  for  a  moment,  on  one 
side,  even  when  surmounted  by 'a  considerable  weight; 
but  as  it  is  only  raised  a  very  little,  and  falls  again  im- 
mediately, the  vase  is  never  open  more  than  an  instant 


462     Inquiries  relative  to  the  Stritcture  of  Wood. 

at  a  time,  and  then  not  so  as  to  admit  the  obtrusion  of 
any  extraneous  matter. 

When  one  of  these  vases  is  put  into  the  stove,  it  is 
placed  upon  a  square  tile,  or  half-brick,  of  burned  earth, 
and  another  of  the  same  kind  is  also  laid  upon  the  cov.er 
to  keep  it  steady. 

During  the  carbonization  of  the  wood,  the  interior 
of  the  vase  is  always  clouded,  assuming  a  very  deep 
blackish-yellow  colour ;  and  during  the  operation  a 
strong  smell  of  soot  or  of  pyroligneous  acid  issues 
from  the  stove ;  which  is  even  insupportable  at  the 
commencement,  if  it  be  too  nearly  approached,  as  well 
as  on  withdrawing  the  vases  from  the  stove,  if  the  covers 
be  removed  without  due  precaution. 

There  is,  therefore,  a  decomposition  during  the  carbon- 
ization of  wood,  and  a  formation  of  pyroligneous  acid. 
This  fact  has  been  long  known ;  but,  in  some  of  my 
experiments,  and  particularly  in  those  made  upon  fir,  with 
a  very  moderate  fire,  I  obtained  a  product,  which,  upon  a 
very  exact  scrutiny,  appeared  to  me  to  be  bitumen. 

This  product  had  been  condensed  upon  the  glass 
cover,  whence  it  had  afterwards  run  in  large  drops  upon 
the  vertical  surface  of  the  side  of  the  vase.  It  was  hard 
and  brittle,  of  a  dark  yellow  colour  ;  it  was  not  affected 
by  boiling  water,  nor  by  boiling  alcohol,  but  was  grad- 
ually dissolved  by  sulphuric  ether. 

It  would  be  superfluous  here  to  enter  upon  the  de- 
tails of  all  my  experiments  relative  to  the  carbonization 
of  wood.  As  the  process  I  have  employed  cannot  now 
but  be  well  known,  after  what  I  have  said  in  this  memoir 
and  in  the  one  that  I  had  the  honour  to  present  to  the 
Class  on  the  joth  of  December  in  last  year,  I  shall  here 
only  give  the  result  of  those  experiments. 


Inqiiiries  relative  to  the  Structure  of  Wood.     463 

The  six  following,  made  with  different  species  of 
wood,  were  so  uniformly  alike  in  their  results,  that  I 
was  much  surprised. 

One  hundred  parts  (10  grammes)  of  the  six  follow- 
ing kinds  of  wood,  in  thin  shavings,  and  thoroughly 
dried,  were  carbonized  at  one  time  in  the  stove,  in  glass 
vases,  well  closed  with  flat  glass  covers.  As  the  heat 
was  managed  with  great  care,  in  order  to  determine 
with  precision,  from  the  weight  of  the  vases,  the  mo- 
ment when  the  operation  was  finished,  the  experiment 
occupied  four  days  and  as  many  nights.  When  the 
vases  with  their  contents  ceased  to  lose  weight,  the  pro- 
cess was  stopped,  and  the  charcoal  was  weighed  while 
still  hot. 

The  following  were  the  results :  — 


100  parts  in  weight  of 

dry  wood 
gave  in   dry  charcoal. 


The  medium  term  of  the  results  of  these  six  experi- 
ments gives  43.33  parts  of  charcoal  in  100  parts  of  dry 
wood ;  and  as  they  were  made  with  woods  differing 
considerably  in  their  apparent  weight,  their  hardness, 
and  other  distinctive  physical  characters,  we  may  con- 
clude, from  the  great  similarity  of  the  results  of  these 
experiments,  that  none  of  the  circumstances  from  which 
the  woods  derive  their  particular  characters  have  any 
material  influence  upon  the  quantities  of  charcoal  they 
are  capable  of  yielding ;  and  hence  we  may  deduce  that 
the  ligneous  substance  or  seerwood,  if  not  the  same  in 
all,  is  at  least  composed  of  identical  substances. 


Poplar 
Lime 

43-571 

)arts. 

Fir     . 
Maple 
Elm 
.  Oak 

44.18 

42-23 
43.27 

43-00 

« 

464     Inquiries  relative  to  the  Structure  of  Wood. 

There  is  still,  however,  a  very  interesting  question  re- 
maining for  discussion,  namely,  Is  the  seerwood  char- 
coal ? 

To  elucidate  this  question,  I  began  by  examining 
whether  charcoal  had  the  same  specific  gravity  as  seer- 
wood. 

I,  therefore,  reduced  some  common  oak-charcoal, 
which  appeared  to  be  well  manufactured,  into  pieces 
about  the  size  of  small  peas,  and  then  boiled  them  in 
a  pretty  good  quantity  of  Seine  water,  previously  well 
filtered  ;  the  pores  of  the  charcoal  were  speedily  so  com- 
pletely filled  with  this  liquid,  that,  becoming  heavier  than 
the  water,  in  equal  bulk,  it  precipitated  itself  to  the  bot- 
tom of  the  vessel,  and  there  remained. 

On  removing  the  vessel  from  the  fire,  the  water  was 
suffered  to  cool  to  the  temperature  of  60°  F. ;  and  then 
the  charcoal,  while  still  submerged,  was  put  into  the 
small  glass  vase  of  the  hydrostatic  balance,  and  weighed. 
Its  weight  in  the  water,  at  the  temperature  of  60°  F., 
was  2.44  grammes. 

When  the  charcoal  was  taken  out  of  the  water,  it  was 
put  into  a  cylindrical  glass  vessel  i^  inch  in  diameter, 
and  6  inches  in  height,  in  which  it  was  thoroughly  dried 
in  the  stove  at  a  temperature  of  about  265°  F. 

After  it  had  been  six  hours  in  the  stove,  it  was  taken 
out  and  weighed  while  still  hot,  and  found  to  be  equal 
to  6.7  grammes ;  therefore  its  specific  gravity  was 

I57,273- 

We  have  before  shown  that  the  specific  gravity  of 

the  solid   parts  of  oak,  in    the  state  of  seerwood,  is 


/*-/•'   I 

This  is  certainly  very  similar  to  that  of  charcoal  made 
of  the  same  kind  of  wood ;  but  we  have  not  yet  proved 


Inquiries  relative  to  the  Structure  of  Wood.     465 

seerwood  to  be  charcoal ;  on  the  contrary,  we  have  just 
seen  that  it  requires  100  parts  of  seerwood  to  obtain 
43-33  Parts  °f  dry  charcoal. 

Neither  is  seerwood  simply  a  hydrure  of  dry  wood, 
as  we  shall  see  in  the  sequel. 

It  should  seem  that  the  fabric  of  a  plant,  which  may 
perhaps  be  nothing  but  pure  charcoal,  is  always  cov- 
ered with  a  substance  analogous  to  the  flesh  which  con- 
ceals the  skeleton  of  an  animal.  This  vegetable  flesh 
does  not  exist  in  considerable  masses ;  for,  as  the 
plant  is  not  under  the  necessity  of  moving  from  one  place 
to  another  in  search  of  nourishment,  it  has  no  need 
either  of  flexible  joints  in  its  skeleton,  nor  of  muscles 
capable  of  exerting  a  great  force ;  and  it  probably  arises 
from  the  circumstances  of  the  skeleton  and  the  flesh 
being  very  intimately  blended  together,  that  they  are  not 
discriminated  and  distinguished  from  each  other. 

I  consider  seerwood  as  the  skeleton  of  the  plant, 
with  the  flesh,  though  quite  dried,  still  adhering  to  it; 
and  as  we  have  seen  that  there  are  43.33  parts  of  char- 
coal in  100  parts  of  seerwood,  I  should  say  that  100 
parts  of  seerwood  are  composed  of 

Charcoal 43.33   parts. 

Vegetable  flesh,  dried 56.67 

Making  together  ....      100.00  parts. 

The  beautiful  analyses  of  Messrs.  Gay-Lussac  and 
Thenard  have  shown  us  that  seerwood  is  composed  of 
carbon,  hydrogen,  and  oxygen  ;  and  that  two  different 
species  of  wood  analyzed  by  them  (the  beech  and  the 
oak)  were  composed  of  these  three  elements  in  nearly 
equal  proportions.  They  also  discovered  that  the  oxy- 
gen and  hydrogen  in  these  woods  are  in  the  requisite 

VOL.    II.  30 


466     Inquiries  relative  to  the  Structure  of  Wood. 

proportions  for  the  formation  of  water ;  wherefore  they 
concluded  that  carbon  was  the  only  combustible  sub- 
stance contained  in  wood. 

It  will  appear  in  the  sequel,  how  well  the  results  of 
these  ingenious  inquiries  accord  with  those  of  my  ex- 
periments. 

But  first,  I  shall  examine  what  quantity  of  charcoal  it 
is  possible  to  obtain  from  different  species  of  woods, 
under  various  degrees  of  dryness,  pursuing  the  method 
already  adopted  in  my  experiments. 

From  the  mode  in  which  charcoal  is  ordinarily  made, 
a  very  considerable  portion  is  lost  and  improvidently 
burned  during  the  operation. 

As  it  appears  to  be  clearly  proved,  by  the  results  of 
the  six  experiments  above  related,  that  the  quantity 
of  charcoal  to  be  obtained  from  any  given  quantity  of 
wood  is  invariably  in  proportion  to  the  quantity  of 
dry  ligneous  substance  contained  in  the  wood,  the  in- 
quiry into  the  quantities  of  charcoal  to  be  produced 
from  different  species  of  woods,  at  various  degrees  of 
dryness,  becomes  limited  to  that  of  the  quantities  of 
wood  absolutely  dry,  contained  in  the  woods  in  question. 

It  has  been  shown  that  100  parts  in  weight  of  oak, 
thoroughly  dried,  give  43  parts  of  charcoal. 

We  have  likewise  seen,  that  100  parts  of  oak  as  dry 
as  it  can  be  made  in  summer,  at  the  temperature  of  62° 
F.,  contain  only  91  parts  of  seerwood,  and,  conse- 
quently, that  100  parts  of  such  wood  would  furnish 
only  39.13  parts  of  charcoal. 

From  the  results  of  an  experiment  of  which  •  I  have 
given  an  account  in  this  memoir,  it  appears  that  100 
parts  of  oak,  in  the  state  wherein  it  is  found  when  ex- 
posed to  the  winter's  air,  at  the  temperature  of  46°  F., 


Inquiries  relative  to  the  Structure  of  Wood.     467 

contain  only  83.36  parts  of  seerwood  ;  consequently, 
100  parts  of  such  wood  would  yield  no  more  than  35.84 
parts  of  charcoal. 

From  the  examination  we  have  made  of  the  oak  in 
that  state  in  which  it  is  deemed  fit  for  burning,  we 
have  found  that  100  parts  of  this  kind  of  wood  contain 
only  76  parts  of  absolutely  dry  wood  ;  whence  we  con- 
clude that  100  parts  of  such  wood  would  produce  32. 68 
parts  of  charcoal. 

It  has  been  shown  that  100  parts  of  an  oak  felled  on 
the  6th  of  September,  while  in  a  growing  state,  contained 
only  62.56  parts  of  seerwood,  and  that,  consequently, 
100  parts  of  such  wood  would  yield  only  26.9  parts  of 
charcoal. 

In  making  these  calculations,  no  account  has  been 
taken  of  the  quantity  of  wood,  or  other  combustible, 
burned  in  order  to  heat  the  closed  vessel  in  which  the 
wood  was  carbonized,  pursuant  to  the  process  here 
adopted.  But  it  may  be  remarked  that  such  quantity 
will  be  increased  or  diminished  according  to  the  con- 
struction of  the  furnace  and  the  arrangement  of  the 
other  parts  of  the  apparatus ;  and  it  will  always  be  too 
considerable  to  be  omitted  in  the  list  of  expenses. 

As  M.  Proust  obtained  only  19  or  20  parts  of  char- 
coal in  100  of  oak,  it  is  probable  that  some  waste 
occurred  in  the  process ;  but  as  it  is  certain  that  in  the 
carbonization  of  wood  some  loss  will  happen,  so  in 
the  ordinary  method  of  making  charcoal  there  is  always 
a  considerable  reduction  of  the  quantity  that  ought  to 
be  produced,  arising  from  the  quantity  of  wood  con- 
sumed, either  wholly  or  in  part,  to  obtain  heat  sufficient 
to  char  the  portion  of  wood  that  is  reduced  to  a  coal. 

Messrs.  Gay-Lussac  and  Thenard  found  from  52  to 


468     Inquiries  relative  to  the  Structure  of  Wood. 

53  parts  of  carbon  in  100  of  seerwood,  but  100  parts 
of  seerwood  yielded  me  only  43  parts  of  charcoal;  this 
difference,  however,  it  is  easy  to  explain,  as  will  be  seen 
in  the  sequel. 

SECTION   VII.  —  Of  the  Quantities    of  Heat  developed  in 
the  Combustion  of  different  Species  of  Wood. 

Many  persons  have  already  endeavoured  to  determine 
the  relative  quantities  of  heat  furnished  by  wood  and 
charcoal  in  their  combustion  ;  but  the  results  of  their 
inquiries  have  not  been  satisfactory.  Their  apparatus 
has  been  too  imperfect,  not  to  leave  vast  incertitude  in 
the  conclusions  drawn  from  their  investigations.  In- 
deed, the  subject  is  so  intricate  in  itself,  that  with  the 
best  instruments  the  utmost  care  is  requisite,  lest,  after 
much  labour,  the  inquirer  should  be  forced  to  content 
himself  with  approximations  instead  of  accurate  results 
and  valuations  strictly  determined. 

All  woods  contain  much  moisture,  even  when  ap- 
parently very  dry ;  and  as  the  persons  alluded  to  have 
neglected  to  determine  the  quantities  of  absolutely  dry 
wood  burned  by  them,  much  uncertainty  prevails  in  the 
results  of  all  their  experiments. 

Another  source  of  uncertainty  lies  in  the  great  quan- 
tity of  heat  suffered  to  escape  with  the  smoke  and  other 
products  of  the  combustion. 

As  the  calorimeter  used  in  my  experiments  has  been 
described  in  a  memoir  which  I  had  the  honour  to  pre- 
sent to  the  Class  on  the  24th  of  February,  1812,  it  is 
unnecessary  here  to  resume  that  subject ;  suffice  it  to 
explain,  in  a  few  words,  the  various  precautions  I 
adopted  in  burning  wood  under  the  calorimeter. 


Inquiries  relative  to  the  Striicture  of  Wood.     469 

I  picked  out  the  woods  intended  for  the  experiment 
from  a  joiner's  workshop,  and  they  all  appeared  to  be 
quite  dry  ;  I  had  them  formed  into  small  boards,  6 
inches  in  length  and  |-  an  inch  thick.  From  these 
boards  I  had  some  shavings  planed  off,  about  ^  of  a 
line  thick,  J  an  inch  broad,  and  6  inches  in  length. 

When  these  shavings  were  sufficiently  dry,  they  were 
burned,  one  by  one,  under  the  mouth  of  the  calorimeter; 
and  I  took  care  to  hold  them,  by  means  of  a  small  pair 
of  nippers,  so  as  to  make  them  burn  with  a  brisk  flame, 
and  without  the  least  smoke  or  smell  or  calculable 
residuum  in  ashes. 

The  following  is  the  method  I  pursued  in  making 
these  experiments. 

The  calorimeter,  filled  with  water  at  a  temperature  of 
about  5°  of  Fahrenheit's  thermometer  lower  than  that  of 
the  apartment  in  which  the  experiments  were  made,  was 
placed  upon  its  stand  at  the  height  of  about  18  inches 
above  the  table  on  which  the  apparatus  was  laid. 

The  extremity  of  the  calorimeter  containing  the  open- 
ing, which  I  call  its  mouth,  projects  about  4  inches  be- 
yond the  edge  of  the  stand,  so  as  easily  to  admit  the 
point  of  the  flame  from  the  small  piece  of  burning 
wood;  and  the  height  of  the  stand  is  so  adjusted  that 
the  operator  may  rest  both  his  elbows  on  the  table, 
while  his  hands  sustain  the  fragment  of  wood  to  be 
burned. 

Near  the  calorimeter  stands  a  small  lamp,  by  which 
the  pieces  of  wood,  or  rather  shavings,  may,  without 
loss  of  time,  be  set  on  fire  and  burned  in  succession  ; 
and  care  is  taken  to  have  always  in  the  hand  a  sufficient 
quantity  of  the  shavings,  of  a  known  weight. 

The  very  small  portions  of  the  shavings  which  remain 


470     Inquiries  relative  to  the  Structure  of  Wood. 

between  the  nippers  are  carefully  preserved,  and  weighed 
at  the  close  of  the  experiments,  to  determine  precisely 
how  much  of  the  wood  has  been  consumed. 

An  assistant  keeps  his  eye  constantly  on  the  ther- 
mometer attached  to  the  apparatus,  and  announces  the 
moment  when  the  water  in  the  calorimeter  has  attained 
a  temperature  as  much  higher  than  that  of  the  room  as 
it  was  below  it  at  the  beginning  of  the  operation  ;  and 
the  flame  from  the  piece  of  wood  then  burning  is  imme- 
diately blown  out. 

The  remains  of  the  shaving  are  laid  aside,  to  be  after- 
wards weighed  with  the  other  fragments. 

The  water  in  the  calorimeter  was  then  stirred,  by 
shaking  it,  taking  care  to  hold  the  instrument  by  its 
wooden  frame,  and  the  temperature  of  the  water  was 
minutely  observed  and  set  down  in  a  register. 

An  experiment  of  this  kind  usually  occupies  about 
10  or  12  minutes,  according  to  the  nature  of  the  wood 
and  the  number  of  degrees  to  which  the  temperature  of 
the  calorimeter  is  raised. 

I  made  choice  of  the  birch  for  my  first  experiments, 
because  the  texture  of  its  wood  is  very  firm  and  even, 
and  burns  with  a  very  regular  flame. 

To  give  the  details  and  their  results  in  few  words,  I 
have  placed  them  together  in  the  subjoined  table. 

The  calorimeter,  with  the  water  it  contained,  was 
equal  in  capacity,  as  to  heat,  to  2781  grammes  of  water. 


Inquiries  relative  to  the  Structure  of  Wood.     471 


Heal  developed  in  the  Combustion  of  Birch  Wood. 


|  No.  of  exp. 

Quantity  of 

wood  consumed. 

Heat  communi- 
cated to  the 
calorimeter. 

Result. 
With  the  heat  developed  in  combustion 
of  i  pound  of  combustible 

Pounds  ol  water          Pounds  of  water 
heated    1°  of       at  the  temperature  of 
Fahrenheit's          melting  ice,  thrown 
thermometer.     |         into  ebullition. 

Grms. 

Degr's. 

Firewood,  2  years  old 

I 

5.00 

10$ 

I       C87C     -1 

32.445 

2 

4.00 

8i 

(                 J         /    J             j 

32.841 

Shavings  dried  in  the  air 

3 

4-55 

10} 

|       6261      \ 

34.805 

"            "            " 

4 

4-54 

10} 

34.881 

Shavings     highly    dried 

over  a  chafing-dish   . 

5 

3-97 

10 

}                        \ 

38.916 

Shavings     highly    dried 

over  a  chafing-dish   . 

6 

2.58 

6* 

\       7002     \ 

38.925 

Shavings     highly    dried 

over  a  chafing-dish   . 

7 

4-97 

I2i 

J                         I 

38.858 

Shavings     highly    dried 

and  scorched  in  a  stove 

8 

5.07 

10} 

3I-325 

Shavings    highly    dried 

and  scorched  in  a  stove 

9 

5.10 

10} 

. 

31.052 

Shavings   scorched,  but 

not  to  so  high  a  degree 

10  4.89 

lOj 

5971 

33.174 

On  comparing  the  results  of  these  six  experiments, 
all  made  with  the  same  kind  of  wood,  in  thin  shavings, 
it  will  appear  that  the  drier  the  wood,  the  greater  was  the 
quantity  of  heat  produced  from  a  given  weight  of  shav- 
ings. But  I  found,  in  taking  account  of  the  quantities 
of  moisture  contained  in  the  woods,  the  quantities  of 
heat  were  always  sensibly  proportional  to  those  of  the 
dry  wood  burned,  with  the  exception,  however,  of  the 
three  latter  experiments,  which  were  made  with  wood 
highly  dried  for  24  hours  in  a  stove,  and  which  gave 
several  indications,  by  no  means  equivocal,  of  the  be- 
ginning of  a  decomposition. 

The  shavings  most  scorched  in  the  stove  gave  less 


472     Inquiries  relative  to  the  Structure  of  Wood. 

heat  than  those  which  had  been  less  scorched  ;  the  two 
sorts  being  taken  in  equal  weights. 

In  all  these  experiments  more  or  less  water  dripped 
from  the  worm,  a  certain  proof  that  some  hydrogen  had 
been  burned  ;  this  fact  I  was  very  desirous  to  verify,  on 
account  of  its  great  importance  to  science. 

It  is  not,  therefore,  mere  carbon  which  furnished  all 
the  heat  developed  in  the  combustion  of  woods  ;  of  this 
important  fact  we  shall  shortly  have  an  additional  proof. 

As  the  great  quantity  of  nitrogen  carried  along  with 
the  products  of  the  combustion,  and  which,  after  having 
passed  through  the  worm,  was  lost  in  the  atmosphere, 
also,  without  doubt,  took  with  it  a  little  more  moisture 
than  it  had  brought  into  the  apparatus,  a  calculation  of 
the  quantity  of  water  formed  in  the  combustion  of  wood, 
grounded  only  on  that  found  in  the  worm,  would  be  erro- 
neous, though  there  was  always  considerably  more  than 
necessary  to  demonstrate  that  water  had  been  formed. 

Before  we  close  this  paper,  we  shall  point  out  a  mode 
whereby  the  quantity  of  water  thus  formed  may  be 
estimated,  even  to  such  a  degree  of  precision  as  to  leave 
nothing  more  to  be  desired.  But  it  is  first  necessary  to 
determine  the  quantity  of  heat  developed  in  the  com- 
bustion of  the  carbon  found  in  this  wood,  and  which 
was  totally  consumed. 

Although  our  experiments  on  the  carbonization  of 
wood,  in  close  vessels,  by  a  moderate  fire,  leave  no 
doubt  as  to  the  quantities  of  charcoal  which  the  woods 
therein  employed  were  capable  of  producing,  still  the 
knowledge  of  this  fact  is  not  alone  sufficient  to  enable 
us  to  determine  the  quantity  of  carbon  contained  in  the 
wood. 

As  100  parts  of  wood  are  required  for  43  of  charcoal, 


Inquiries  relative  to  the  Structure  of  Wood.     473 

it  is  evident  that  the  seerwood  is  at  least  partially  de- 
composed when  the  charcoal  is  produced  in  the  process 
of  carbonization,  that  is  to  say,  when  the  skeleton  of 
the  wood  is  deprived  of  its  flesh,  and  left  naked ;  and 
it  is  well  known  that  a  great  quantity  of  pyroligneous 
acid  is  formed  in  the  carbonization  of  wood,  and  this 
acid  contains  carbon. 

From  the  process  employed  by  Messrs.  Gay-Lussac 
and  Thenard,  in  their  learned  analysis,  there  can  be  no 
doubt  that  they  discovered  and  kept  an  account  of  all 
the  carbon  found  in  the  woods  analyzed  by  them  ;  and 
as  there  was  no  pyroligneous  acid  formed  in  my  experi- 
ments when  the  wood  was  totally  consumed  without 
either  smoke  or  smell,  it  is  manifest  that  in  this  case  all 
the  carbon  contained  in  the  wood  was  burned. 

According  to  the  analyses  of  Messrs.  Gay-Lussac  and 
Thenard,  100  parts  of  oak,  perfectly  dry,  contain  52.54 
parts  of  carbon  ;  and  100  parts  of  beech  contain  51.45. 

Now,  as  it  seems  to  me  extremely  probable  that  the 
dry  ligneous  substance  is  palpably  the  same  in  all  woods, 
I  shall  take  the  medium  term  of  the  results  of  these 
two  analyses,  and  consider  it  as  an  indubitable  fact,  that 
100  parts  of  perfectly  dry  wood  contain  52  parts  of 
carbon. 

Therefore,  as  100  parts  of  seerwood  furnished  me 
with  only  43  of  charcoal,  we  must  conclude,  if  dry  char- 
coal be  considered  as  carbon,  that  of  the  52  parts  of 
carbon  contained  in  100  parts  of  seerwood,  9  are  taken 
up  in  the  composition  of  the  pyroligneous  acid  formed 
in  the  carbonization  of  the  wood,  which  9  parts  make 
more  than  17  per  cent  of  all  the  carbon  contained  in 
the  wood. 

Though  charcoal  should   not  be   purely  carbon,  we 


474     Inquiries  relative  to  the  Structure  of  Wood. 

must,  nevertheless,  admit  that  there  is  still  a  much 
greater  proportion  of  carbon  employed  in  the  formation 
of  that  acid,  or  of  other  substances  which  fly  off  into  the 
atmosphere  during  the  process  of  the  carbonization  of 
the  wood. 

In  pursuing  inquiries  in  natural  philosophy,  the  first 
object  that  demands  attention  is  to  keep  an  accurate 
account  of  weights  ;  and  so  long  as  we  proceed  with  the 
balance  in  hand,  there  is  little  hazard  of  being  misled. 

And  here,  before  I  proceed  further  in  the  inquiry  into 
the  sources  of  the  heat  developed  during  the  combustion 
of  wood,  I  shall  exhibit  a  general  table  of  the  details  and 
results  of  forty-three  experiments  made  upon  eleven  dif- 
ferent kinds  of  the  woods  of  our  climate.  As  I  shall  have 
occasion  to  refer  to  some  of  these  experiments  for  the 
establishment  of  facts,  it  is  requisite  that  they  should 
first  be  known. 

All  these  experiments  having  been  made  and  registered 
long  before  I  began  the  calculations  ultimately  adopted 
for  the  elucidation  of  their  results,  I  have  not  hesitated 
to  rely  on  them.  And  further,  as  they  were  made  with 
all  possible  care,  and  with  instruments  to  me  apparently 
perfect,  I  can  answer  for  their  accuracy. 

New  experiments  ever  bear  a  certain  value  ;  all  the 
knowledge  which  constitutes  the  imperishable  riches  of 
mankind  consists  only  of  accurate  statements  of  well- 
conducted  experiments.  Happy  they  who  have  the 
good  fortune  of  contributing  something  to  the  general 
stock ! 


Inquiries  relative  to  the  Stmcture  of  Wood.    475 

Heat  developed  in  the  Combustion  of  various  Species  of  Wood. 


Species  of 
wood. 

Quality. 

Number  of  the  experiment. 

Quantity  of  wood  burned. 

Heat  communicated  to  the 
calorimeter  whose  capac- 
ity was  equal  to  2781 
grammes  of  water. 
Quantity  of  water  at  the 
thawing  temperature, 
boiled  by  the  neat  de- 
veloped in  the  combus- 
tion of  one  pound  of 
combustible. 

Grms. 

Degr's. 

Pounds. 

Lime 

Joiner's  dry  wood,  4  years  old 

(II 

(  I2 

4.52 

4-55 

34.609 
34-805 

Same  kind  highly  dried  over  a 
chafing-dish                             • 

1*3 
(14 

4.06 
3.80 

IOJ 

10 

40^58 

Same  kind,  rather  less  dried  . 

15 

5-57 

14 

38.833 

Beech 

Joiner's  dry  wood,  4  or  5  years 
old      

(16 

4-74 

io| 

33-817 

(17 

4.72 

I0i 

33-752 

Same  kind,  highly  dried  over  a 
chafing-dish                  • 

(18 

(19 

5.07 
4-43 

12 

I  Of 

36.334 
36.184 

Elm 

oiner's  wood,  rather  moist    . 

20 

6-34 

1  'i 

27.147 

oiner's  dry  wood,  4  or  5  years 
old      

(21 

5.28 

I  Of 

30359 

(22 

5-45 

I  °f 

30.051 

Same  kind,  highly  dried  over 

(24 

4-70 
5.28 

I°i 

II.1, 

34-5  '5 
33-651 

Same  kind,  dried  and  scorched 

in  the  stove       ..... 

2C 

A    QO 

8 

3O.QOO 

Oak 

Common  firewood,  in  moder- 

T'w 

j^-y 

26 

.     0. 

8 

2C.CQO 

Same  kind  in  thicker  shavings  ; 

' 

j  j  y 

leaving  a  residuum  of  charcoal 

27 

6.40 

10* 

24.748 

Same  kind  in  thin  shavings    . 

28 

6.14 

26.272 

Same  kind,  thin  shavings,  well 

dried  in  the  air      .... 

29 

7.22 

13 

29.210 

[oiner's   wood,   very  dry,   in 
thin  shavings    

(30 
(31 

5-3° 

5-33 

10} 

29.880 
19.796 

Ash 

Thick    shavings,  leaving   0.92 
gramme  of  charcoal    .     .     . 
Joiner's  common  dry  wood    . 

32 
33 

6.48 
5.29 

II 

10.1 

26.227 
30.666 

Same  kind,  shavings  dried   in 

the  sir                     •     •     •     • 

1.A 

3.78 

81 

33.720 

Same  kind,  highly  dried  over 

Jl 

J    1 

4 

a  chafing-dish   

35 

5-23 

12 

35-449 

476     Inquiries  relative  to  the  Structure  of  Wood. 

Heat  developed  in  the  Combustion  of  Wood.      (Continued.) 


"c 

1 

1 

|lt 

!W^ 

'« 

1 

isss 

Zllll 

Species  of 
wood. 

Quality. 

U 

•8 

•a 

||  H 

ll|lsd 

1 

X 

l|i| 

.f.S-gl^J 

fc 

I 

^"S  -  u 
ffi 

pill 

Grms. 

Degr's. 

Pounds. 

Maple 

Seasoned   wood,    highly   dried 

over  a  chafing-dish 

36 

3.85 

9 

36.117 

Service 

Same  kind 

1  7 

36.  1  30 

Same  kind,  scorched  in  a  stove 

51 

38 

4-3° 

9 

32.337 

Cherry 

Joiner's  dry  wood   .... 

39 

4-75 

33-339 

Same  kind,  highly  dried  over 

a  chafing-dish    

4-O 

4-16 

IC^ 

36.QO4 

Same  kind,  scorched  in  a  stove 

T 

41 

T    J  v 

5.00 

HJL 

j  w  y   T~ 

34-763 

Fir 

Joiner's  common  dry  wood    . 

42 

5-35 

I0i 

30.322 

Shavings,  well  dried  in  the  air 

43 

4.09 

Q 

34.000 

Highly  dried   over  a  chafing- 

dish 

A  A 

3  72 

37  37Q 

Dried  and  scorched  in  a  stove 

TT 

45 

j*/  * 

4.40 

j  /  •  j  /  y 

33-358 

Thick  shavings,  leaving  much 

charcoal 

4.6 

4r  i 

6i 

28  6cK 

Poplar 

Joiner's  common  dry  wood    . 

T" 

47 

•3  * 

4-'3 

9i 

"^J 

34.601 

Same  kind,  highly  dried  over  a 

chafing-dish                        •     • 

4-8 

3.QC 

qi 

77    T  f\  T 

Hornbeam 

Joiner's  dry  wood    .      . 

T" 

(49 

(5° 

j  y  j 

5.01 

ya 

I0l 

31.800 
31.609 

Oak 

Dried  to  {8l'JW°°rJ   imper- 

fectly burned,  leaving  a  resid- 

uum    of    charcoal,     in     the 

combustion,  of  o.  8  1  gramme 

51 

6.i4 

ioi 

26.421 

0.73        « 

52 

4-83 

8" 

25.591 

0.94       " 

53 

6.71   u 

25.917 

These  experiments  might  lead  to  a  great  number  of 
observations  ;  but  I  shall  endeavour  to  reduce  them  to 
the  exposition  of  a  few  simple  facts  which  they  pre- 
sent. 

One  fact,  certainly  very  curious  and  of  the  first  im- 
portance to  the  knowledge  of  the  vegetable  economy, 


Inquiries  relative  to  the  Structure  of  Wood.    477 

appears  to  be  well  established  ;  namely,  that  the  skele- 
ton of  trees  is  pure  charcoal,  and  that  it  exists  in  a 
perfect  state  in  wood. 

If  this  charcoal  did  not  exist  perfectly  formed  in 
wood,  it  could  not  possibly  preserve  its  form,  while  its 
envelope  of  vegetable  flesh  is  destroyed  by  the  fire  in 
the  process  of  carbonization. 

As  the  vegetable  flesh  contains  hydrogen  as  well  as 
carbon,  it  is  more  inflammable  than  charcoal,  and  is  con- 
sumed at  a  lower  temperature;  and,  by  proper  manage- 
ment of  the  fire,  it  may  be  totally  destroyed  without  the 
enclosed  skeleton  of  charcoal  being  injured. 

Some  months  ago  I  presented  the  Class  with  a  small 
sprig  of  charcoal  produced  from  a  piece  of  oak  partially 
burned  under  my  calorimeter.  It  was  nearly 'all  the 
charcoal  contained  in  the  piece.  All  the  coal  or  flesh 
of  the  wood  burned  with  a  brisk  flame,  and  the  skeleton 
of  the  wood  had  got  red,  but  the  heat  was  not  sufficient 
to  consume  it. 

The  charcoal-maker  seldom  does  more  than  burn  the 
flesh  of  the  wood,  and  leaves  the  skeleton  of  charcoal 
naked. 

The  dry  vegetable  flesh  produces  more  heat  in  its 
combustion  than  an  equal  weight  of  dry  charcoal. 

Shavings  scorched  in  the  stove  by  a  great  heat  yield 
less  heat  in  their  combustion  than  shavings  of -the  same 
kind  of  wood,  whose  vegetable  flesh  has  not  been 
touched.  See  experiments  Nos.  5,  6,  7,  8,  9,  10,  25, 

38,  41,  45- 

In  tables  of  experiments  similar  to  those  registered  in 
the  preceding  table,  it  is  scarcely  possible  to  have  errors 
on  the  greater  side  ;  but  they  may  easily  enough  happen 
on  the  lesser.  We  may,  therefore,  place  the  more  con- 


478     Inquiries  relative  to  the  Structure  of  Wood. 

fidence  in  those  wherein  the  quantities  of  heat  manifested 
have  been  the  greatest. 

In  the  experiments  Nos.  13  and  14,  the  wood  of  the 
lime-tree,  dried  over  a  chafing-dish,  was  productive  of 
more  heat  than  any  other  wood  that  I  examined. 

The  result,  it  will  be  seen,  was  for  i  pound  of  this 
wood  burned  in  experiment, 

No.  13  .         .     39.605  pounds  of  water  heated  180°  F.,  and  in 

No.  14      .         .         40.658  "  "       " 


Medium         .         .40.1315 

In  order  accurately  to  ascertain  how  much  water  this 
wood  contained,  I  dried  thoroughly  in  the  stove  a  parcel 
of  shavings  which  had  been  previously  dried  over  the 
chafing-dish,  and  found  that  it  still  retained  6.977  per 
cent  of  water. 

Therefore  we  may  conclude  that  i  pound  of  this 
wood  contains  only  0.93023  pound  of  seerwood. 

Now,  if  0.93023  pound  of  seerwood  will  heat  40.- 
1315  pounds  of  water  180°  F.,  i  pound  of  the  same 
wood  ought  to  heat  43.141  pounds;  and  I  therefore 
take  this  quantity  of  water  heated  180°  F.  as  the  stand- 
ard of  the  heat  developed  in  the  combustion  of  i  pound 
of  wood  perfectly  dried. 

Many  persons  have  endeavoured  to  account  for  the 
heat  manifested  in  the  combustion  of  wood,  by  attrib- 
uting it  altogether  to  the  charcoal  contained  in  the  wood 
burned. 

This  hypothesis  we  have  now  to  examine. 

It  has  been  seen,  that  100  parts  of  the  wood  of  the 
lime-tree,  perfectly  dried,  yielded  43.59  Parts  °f  char- 
coal ;  consequently  i  pound  of  this  wood,  thoroughly 
dried,  can  contain  only  0.4359  pound  of  charcoal. 


Inquiries  relative  to  the  Striicture  of  Wood.     479 

According  to  the  results  of  Crawford's  experiments, 
which  we  have  found  to  be  very  accurate,  i  pound  of 
charcoal  furnishes  in  its  combustion  only  the  necessary 
heat  for  raising  57.608  pounds  of  water  180°  F. ;  there- 
fore the  charcoal  contained  in  i  pound  of  dry  lime-wood, 
equal  to  0.4359  pound,  can  furnish  in  its  combustion  no 
more  heat  than  is  necessary  to  raise  25.111  pounds  of 
water  180°;  but  as  the  experiment  has  given  43.141 
pounds,  there  must  certainly  have  been  some  other  sub- 
stance burned  beside  the  charcoal,  and  which  could  have 
been  none  other  than  hydrogen. 

Before  we  determine  the  quantity  of  hydrogen  con- 
sumed, it  is  essential  to  ascertain  how  much  heat  has 
been  furnished,  not  merely  by  the  charcoal  itself,  but 
by  the  charcoal  and  the  carbon  contained  in  the  wood ; 
for  it  is  very  certain  that  all  the  carbon  was  burned, 
since  no  pyroligneous  acid  was  formed. 

According  to  the  analyses  of  Messrs.  Gay  Lussac  and 
Thenard,  i  pound  of  dry  wood  contains  0.52  pound  of 
carbon. 

If  we  adopt  Crawford's  estimate,  we  shall  find  that 
the  combustion  of  0.52  pound  of  carbon  ought  to  fur- 
nish heat  sufficient  to  raise  29.956  pounds  of  water 
1 80°  F. 

Deducting  this  quantity  of  water  from  that  given  by 
the  experiment,  namely,  43.141  pounds,  we  shall  have 
13.185  pounds  as  the  measure  of  the  heat  produced  by 
the  combustion  of  the  hydrogen  consumed  in  the  experi- 
ment. 

From  the  results  of  this  inquiry  we  may  conclude,  that 
of  the  heat  manifested  in  the  combustion  of  wood, 
rather  more  than  two  thirds  are  produced  by  the  com- 
bustion of  the  carbon,  and  a  little  less  than  one  third  by 
the  hydrogen  consumed. 


480     Inquiries  relative  to  the  Structure  of  Wood. 

These  data  supply  us  with  an  easy  method  of  deter- 
mining the  quota  of  free  and  combustible  hydrogen  con- 
tained in  seerwood. 

According  to  Crawford's  estimate,  which  we  have  fol- 
lowed all  along,  i  pound  of  hydrogen  yields  in  its 
combustion  heat  sufficient  to  raise  410  pounds  of  water 
180°  F.  ;  therefore,  the  13.185  pounds  heated  180°  in 
the  experiment  in  question  must  have  required  0.035158 
pound  of  hydrogen,  which  is  consequently  the  amount 
of  free  and  combustible  hydrogen  contained  in  i  pound 
of  seerwood. 

Assuming  the  medium  term  of  the  results  of  the  two 
analyses  of  dry  wood,  made  by  Messrs.  Gay  Lussac  and 
Thenard,  i  pound  of  seerwood  would  be  composed  of 

Carbon          .......     0.52  pound. 

Hydrogen  and  oxygen,  in  the  necessary  pro- 
portions for  forming  water  .          .  0.48 

i. oo 

From  the  result  of  my  experiments,  i  pound  of  seer- 
wood is  composed  of  two  distinct  substances  ;  namely,  — 

A  skeleton  of  charcoal  weighing     .         .         .     0.43  pound. 
Vegetable  flesh 0.57 


And   these  0.57   pound   of  vegetable  flesh  are  com- 
posed of 

Carbon,  free  and  combustible       .          .          .  0.090  pound. 
Hydrogen,  free  and  combustible        .          .  °«°35 
Hydrogen  and  oxygen,  in  the  necessary  pro- 
portions for  the  formation  of  water  .         .  0.445 


Inquiries  relative  to  the  Structure  of  Wood.     48 1 

In  making  these  estimates,  I  have  availed  myself  of 
the  valuation  of  the  total  quantity  of  carbon  contained 
in  seerwood,  given  in  the  analysis  of  Messrs.  Gay 
Lussac  and  Thenard  ;  and  I  have  supposed  the  43  per 
cent  of  charcoal,  which  I  found  to  be  contained  in  seer- 
wood,  to  be  pure  carbon. 

Should  it  ultimately  appear  that  charcoal  is  not  pure 
carbon,  which  is  extremely  probable,  numerous  altera- 
tions in  all  these  estimates  must  follow,  though  the  ex- 
periments made  upon  the  woods  will  always  retain  their 
value.  And  I  cannot  but  hope  that  they  will  be  fre- 
quently repeated,  with  such  variations  as  may  conduce  to 
important  discoveries. 

It  will  be  a  satisfaction  to  me  to  know  that  I  have 
put  into  the  hands  of  more  skilful  workmen  than  my- 
self some  instruments  of  which  they  may  advanta- 
geously avail  themselves  :  and  to  have  pointed  out,  as 
well  as  a  little  smoothed,  a  new  path,  wherein  they  may 
walk  without  danger  of  being  lost. 

SECTION  VIII.  —  Of  the  Quantity  of  Heat  lost  in  the  Car- 
bonization of  Wood. 

In  making  charcoal,  a  considerable  quantity  of  heat 
is  dissipated  and  lost  in  the  air;  whence  it  is  evident 
that  the  same  amount  of  heat  cannot  be  obtained  from 
burning  a  given  quantity  of  charcoal  as  would  be  fur- 
nished by  the  combustion  of  the  wood  of  which  it  is 
formed. 

We  can  now  determine,  with  great  precision,  the  loss 
of  heat  which  is  inevitable  in  making  charcoal,  even 
when  all  possible  precautions  have  been  taken;  as  well 
as  that  which  happens  every  day  in  the  process  employed 
by  the  charcoal-maker. 


482     Inquiries  relative  to  the  Structure  of  Wood. 

As  the  combustion  of  i  pound  of  charcoal,  perfectly 
dry,  yields  heat  sufficient  to  boil  57.608  pounds  of 
water,  at  the  thawing  temperature  ;  and  as  I  pound  of 
wood,  thoroughly  dry,  furnishes  0.4333  pound  of  dry 
charcoal,  it  follows,  that  the  charcoal  produced  from  i 
pound  of  dry  wood  should  furnish  in  its  combustion 
heat  sufficient  to  boil  24.958  pounds  of  water,  at  the 
thawing  temperature. 

But  we  have  already  seen  that  the  combustion  of 
i  pound  of  wood,  thoroughly  dry,  should  furnish  suffi- 
cient heat  to  boil  43.143  pounds  of  water  at  the  freezing 
temperature ;  or,  which  is  the  same  thing,  to  raise  it 
1 80°  of  Fahrenheit's  thermometer. 

These  two  numbers  (43.143  and  24.958),  which  ex- 
press the  quantities  of  heat  in  question,  being  in  the 
proportion  of  100  to  57.849,  it  is  evident  that  the  loss 
of  heat  inevitable  in  the  carbonization  of  wood  is  up- 
wards of  42  per  cent,  or  exactly  42.151  per  cent  of  the 
total  quantity  that  the  wood  will  furnish. 

In  order  to  determine  the  loss  of  heat  which  occurs 
in  the  forests,  by  the  ordinary  process  of  the  charcoal- 
burner,  it  is  requisite  to  ascertain  the  precise  product 
of  charcoal  from  a  given  quantity  of  wood,  though  it  is 
probable  that  this  product  is  very  variable.  M.  Proust 
estimates  it  at  20  per  cent  in  weight  at  the  highest. 

Adopting,  for  a  moment,  this  estimate,  and  suppos- 
ing the  carbonized  wood  in  the  same  state  of  dryness  as 
what  is  usually  sold  for  firewood  ;  as  100  pounds  of  such 
wood  contains  only  0.76  pound  of  perfectly  dry  wood, 
this  quantity  would  furnish  in  its  combustion  only  the 
degree  of  heat  necessary  to  raise  32.043  pounds  of 
water  180°  F. 

But  the  0.20  pound  of  charcoal  produced  by  the  car- 


Inquiries  relative  to  the  Structure  of  Wood.     483 

bonization  of  I  pound  of  this  wood,  according  to  the 
usual  process,  can  only  furnish  by  combustion  a  suffi- 
cient quantity  of  heat  to  raise  11.521  pounds  of  water 
180°  F.  ;  and  as  the  numbers  32.043  and  11.521  are 
nearly  in  the  proportion  of  100  to  36,  it  should  seem 
that  the  loss  of  heat  in  question  is  about  64  per  cent. 

One  very  important  fact,  which  appears  to  be  well 
ascertained  by  the  results  of  this  inquiry,  is,  that  all  the 
charcoal  produced  from  the  carbonization  of  3  pounds 
of  any  kind  of  wood  scarcely  gives  more  heat  in  its 
combustion  than  would  be  furnished  by  i  pound  of  the 
same  sort  of  wood  burned,  and  in  its  natural  state. 

[This  paper  is  printed  from  Nicholson's  Journal,  XXXIV.  (1813), 
PP-  3I9~325»  and  XXXV.,  pp.  95-117.] 


CHIMNEY     FIREPLACES, 


PROPOSALS  FOR  IMPROVING  THEM  TO  SAVE  FUEL; 
TO  RENDER  DWELLING-HOUSES  MORE  COMFORT- 
ABLE AND  SALUBRIOUS,  AND  EFFECTUALLY  TO 
PREVENT  CHIMNEYS  FROM  SMOKING. 


CHAPTER    I. 

Fireplaces  for  burning  Coals,  or  Wood,  in  an  open  Chimney, 
are  capable  of  great  Improvement.  —  Smoking  Chimneys 
may  in  all  cases  be  completely  cured.  —  The  immoderate 
Size  of  the  Throats  of  Chimneys  the  principal  Cause  of  all 
their  Imperfections.  —  Philosophical  Investigation  of  the 
Subject.  —  Remedies  proposed  for  all  the  Defects  that  have 
been  discovered  in  Chimneys  and  their  open  Fireplaces.  — 
These  Remedies  applicable  to  Chimneys  destined  for  burning 
Wood,  or  Turf,  as  well  as  those  constructed  for  burning 
Coals. 

THE  plague  of  a  smoking  chimney  is  proverbial; 
but  there  are  many  other  very  great  defects  in  open 
fireplaces,  as  they  are  now  commonly  constructed  in 
this  country,  and  indeed  throughout  Europe,  which, 
being  less  obvious,  are  seldom  attended  to ;  and  there 
are  some  of  them  very  fatal  in  their  consequences  to 
health  ;  and,  I  am  persuaded,  cost  the  lives  of  thou- 
sands every  year  in  this  island. 

Those  cold  and  chilling  draughts  of  air  on  one  side 
of  the  body  while  the  other  side  is  scorched  by  a  chim- 


Of  Chimney  Fireplaces.  485 

ney  fire,  which  every  one  who  reads  this  must  often 
have  felt,  cannot  but  be  highly  detrimental  to  health, 
and  in  weak  and  delicate  constitutions  must  often  pro- 
duce the  most  fatal  effects.  I  have  not  a  doubt  in  my 
own  mind  that  thousands  die  in  this  country  every  year 
of  consumptions  occasioned  solely  by  this  cause,  —  by  a 
cause  which  might  be  so  easily  removed  ! — by  a  cause 
whose  removal  would  tend  to  promote  comfort  and  con- 
venience in  so  many  ways  ! 

Strongly  impressed  as  my  mind  is  with  the  impor- 
tance of  this  subject,  it  is  not  possible  for  me  to  remain 
silent.  The  subject  is  too  nearly  connected  with  many 
of  the  most  essential  enjoyments  of  life  not  to  be  highly 
interesting  to  all  those  who  feel  pleasure  in  promoting 
or  in  contemplating  the  comfort  and  happiness  of  man- 
kind. And  without  suffering  myself  to  be  deterred 
either  by  the  fear  of  being  thought  to  give  to  the  sub- 
ject a  degree  of  importance  to  which  it  is  not  entitled, 
or  by  the  apprehension  of  being  tiresome  to  my  readers 
by  the  prolixity  of  my  descriptions,  I  shall  proceed 
to  investigate  the  subject  in  all  its  parts  and  details  with 
the  utmost  care  and  attention.  And  first  with  regard 
to  smoking  chimneys. 

There  are  various  causes  by  which  chimneys  may  be 
prevented  from  carrying  smoke,  but  there  are  none  that 
may  not  easily  be  discovered  and  completely  removed. 
This  will  doubtless  be  considered  as  a  bold  assertion  ;  but 
I  trust  I  shall  be  able  to  make  it  appear  in  a  manner  per- 
fectly satisfactory  to  my  readers  that  I  have  not  ventured 
to  give  this  opinion  but  upon  good  and  sufficient 
grounds. 

Those  who  will  take  the  trouble  to  consider  the  na- 
ture and  properties  of  elastic  fluids,  of  air,  smoke,  and 


486  Of  Chimney  Fireplaces. 

vapour,  and  to  examine  the  laws  of  their  motions,  and 
the  necessary  consequences  of  their  being  rarified  by 
heat,  will  perceive  that  it  would  be  as  much  a  miracle 
if  smoke  should  not  rise  in  a  chimney,  all  hindrances 
to  its  ascent  being  removed,  as  that  water  should  refuse 
to  run  in  a  syphon,  or  to  descend  in  a  river. 

The  whole  mystery,  '  therefore,  of  curing  smoking 
chimneys,  is  comprised  in  this  simple  direction ;  find 
out  and  remove  those  local  hindrances  which  forcibly  prevent 
the  smoke  from  -following  its  natural  tendency  to  go  up  the 
chimney ;  or  rather,  to  speak  more  accurately,  which  pre- 
vent its  being  forced  up  the  chimney  by  the  pressure 
of  the  heavier  air  of  the  room. 

Although  the  causes  by  which  the  ascent  of  smoke  in 
a  chimney  may  be  obstructed  are  various,  yet  that  cause 
which  will  most  commonly,  and  I  may  say  almost  uni- 
versally, be  found  to  operate,  is  one  which  it  is  always 
very  easy  to  discover,  and  as  easy  to  remove,  —  the  bad 
construction  of  the  chimney  in  the  neighbourhood  of  the 
fireplace. 

In  the  course  of  all  my  experience  and  practice  in 
curing  smoking  chimneys,  —  and  I  certainly  have  not 
had  less  than  five  hundred  under  my  hands,  and  among 
them  many  which  were  thought  to  be  quite  incurable,  — 
I  never  have  been  obliged,  except  in  one  single  instance, 
to  have  recourse  to  any  other  method  of  cure  than 
merely  reducing  the  fireplace,  and  the  throat  of  the 
chimney,  or  that  part  of  it  which  lies  immediately  above 
the  fireplace,  to  a  proper  form  and  just  dimensions. 

That  my  principles  for  constructing  fireplaces  are 
equally  applicable  to  those  which  are  designed  for  burn- 
ing coal,  as  to  those  in  which  wood  is  burned,  has  lately 
been  abundantly  proved  by  experiments  made  here  in 


Of  Chimney  Fireplaces.  487 

London  ;  for  of  above  a  hundred  and  fifty  fireplaces 
which  have  been  altered  in  this  city  under  my  direction, 
within  these  last  two  months,  there  is  not  one  which  has 
not  answered  perfectly  well.*  And  by  several  experi- 
ments which  have  been  made  with  great  care,  and  with 
the  assistance  of  thermometers,  it  has  been  demon- 
strated, that  the  saving  of  fuel,  arising  from  these  im- 
provements of  fireplaces,  amounts  in  all  cases  to  more 
than  half)  and  in  many  cases  to  more  than  two  thirds,  of 
the  quantity  formerly  consumed.  Now  as  the  altera- 
tions in  fireplaces  which  are  necessary  may  be  made  at  a 
very  trifling  expense, —  as  any  kind  of  grate  or  stove  may 
be  made  use  of,  and  as  no  iron  work  but  merely  a  few 
bricks  and  some  mortar,  or  a  few  small  pieces  of  fire- 
stone,  are  required, — the  improvement  in  question  is 
very  important  when  considered  merely  with  a  view  to 
economy ;  but  it  should  be  remembered,  that  not  only 
a  great  saving  is  made  of  fuel  by  the  alterations  pro- 
posed, but  that  rooms  are  made  much  more  comfortable, 

*  Eves  and  Sutton,  bricklayers,  Broad  Sanctuary,  Westminster,  have  alone  altered 
above  ninety  chimneys.  The  experiment  was  first  made  in  London  at  Lord  Palmers- 
ton's  house  in  Hanover  Square;  then  two  chimneys  were  altered  in  the  house  of  Sir 
John  Sinclair,  Baronet,  President  of  the  Board  of  Agriculture ;  one  in  the  room  in 
in  which  the  Board  meets,  and  the  other  in  the  Secretary's  room;  which  last  being 
much  frequented  by  persons  from  all  parts  of  Great  Britain,  it  was  hoped  that  circum- 
stance would  tend  much  to  expedite  the  introduction  of  these  improvements  in  various 
parts  of  the  kingdom.  Several  chimneys  were  then  altered  in  the  house  of  Sir  Joseph 
Banks,  Baronet,  K.  B.,  President  of  the  Royal  Society.  Afterwards  a  number  were 
altered  in  Devonshire  House ;  in  the  house  of  Earl  Besborough,  in  Cavendish  Square, 
and  at  his  seat  at  Rockhampton ;  at  Holywell  House,  near  St.  Alban's,  the  seat  of 
the  Countess  Dowager  Spencer;  at  Melbourne  House;  at  Lady  Templeton's,  in  Port- 
land Place;  at  Mrs.  Montagu's,  in  Portman  Square;  at  Lord  Sudley's,  in  Dover 
Street;  at  the  Marquis  of  Salisbury's  seat,  at  Hatfield,  and  at  his  house  in  town;  at 
Lord  Palmerston's  seat  in  Broadlands,  near  Southampton,  and  at  several  gentlemen's 
houses  in  that  neighborhood  ;  and  a  great  many  others ;  but  it  would  be  tiresome  to 
enumerate  them  all,  and  even  these  are  mentioned  merely  for  the  satisfaction  of 
those  who  may  wish  to  make  inquiries  respecting  the  success  of  the  experiments. 


488  Of  Chimney  Fireplaces. 

and  more  salubrious  ;  that  they  may  be  more  equally 
warmed,  and  more  easily  kept  at  any  required  tempera- 
ture ;  that  all  draughts  of  cold  air  from  the  doors  and 
windows  towards  the  fireplace,  which  are  so  fatal  to 
delicate  constitutions,  will  be  completely  prevented ; 
that  in  consequence  of  the  air  being  equally  warm  all 
over  the  room,  or  in  all  parts  of  it,  it  may  be  entirely 
changed  with  the  greatest  facility,  and  the  room  com- 
pletely ventilated  when  this  air  is  become  unfit  for  res- 
piration, and  this  merely  by  throwing  open  for  a  mo- 
ment a  door  opening  into  some  passage  from  whence 
fresh  air  may  be  had,  and  the  upper  part  of  a  window ; 
or  by  opening  the  upper  part  of  one  window  and  the 
lower  part  of  another.  And  as  the  operation  of  venti- 
lating the  room,  even  when  it  is  done  in  the  most  com- 
plete manner,  will  never  require  the  door  and  window 
to  be  open  more  than  one  minute,  in  this  short  time 
the  walls  of  the  room  will  not  be  sensibly  cooled,  and 
the  fresh  air  which  comes  into  the  room  will,  in  a  very 
few  minutes,  be  so  completely  warmed  by  these  walls, 
that  the  temperature  of  the  room,  though  the  air  in  it 
be  perfectly  changed,  will  be  brought  to  be  very  nearly 
the  same  as  it  was  before  the  ventilation. 

Those  who  are  acquainted  with  the  principles  of 
pneumatics,  and  know  why  the  warm  air  in  a  room 
rushes  out  at  an  opening  made  for  it  at  the  top  of  a 
window  when  colder  air  from  without  is  permitted  to 
enter  by  the  door  or  by  any  other  opening  situated 
lower  than  the  first,  will  see  that  it  would  be  quite  im- 
possible to  ventilate  a  room  in  the  complete  and  expedi- 
tious manner  here  described,  where  the  air  in  a  room  is 
partially  warmed,  or  hardly  warmed  at  all,  and  where 
the  walls  of  the  room,  remote  from  the  fire,  are  con- 


Of  Chimney  Fireplaces.  489 

stantly  cold ;  which  must  always  be  the  case  where,  in 
consequence  of  a  strong  current  up  the  chimney,  streams 
of  cold  air  are  continually  coming  in  through  all  the 
crevices  of  the  doors  and  windows,  and  flowing  into  the 
fireplace. 

But  although  rooms  furnished  with  fireplaces  con- 
structed upon  the  principles  here  recommended,  may  be 
easily  and  most  effectually  ventilated  (and  this  is  cer- 
tainly a  circumstance  in  favour  of  the  proposed  im- 
provements), yet  such  total  ventilations  will  very  sel- 
dom, if  ever,  be  necessary.  As  long  as  any  fire  is  kept 
up  in  the  room,  there  is  so  considerable  a  current  of  air 
up  the  chimney,  notwithstanding  all  the  reduction  that 
can  be  made  in  the  size  of  its  throat,  that  the  continual 
change  of  air  in  the  room  which  this  current  occasions 
will,  generally,  be  found  to  be  quite  sufficient  for  keep- 
ing the  air  in  the  room  sweet  and  wholesome ;  and,  in- 
deed, in  rooms  in  which  there  is  no  open  fireplace,  and 
consequently  no  current  of  air  from  the  room  setting 
up  the  chimney, —  which  is  the  case  in  Germany  and  all 
the  northern  parts  of  Europe,  where  rooms  are  heated 
by  stoves,  whose  fireplaces,  opening  without,  are  not  sup- 
plied with  the  air  necessary  for  the  combustion  of 
the  fuel  from  the  room  ;  and  although  in  most  of  the 
rooms  abroad,  which  are  so  heated,  the  windows  and 
doors  are  double,  and  both  are  closed  in  the  most  exact 
manner  possible,  by  slips  of  paper  pasted  over  the  crevi- 
ces, or  by  slips  of  list  or  fur,  yet  when  these  rooms  are 
tolerably  large,  and  when  they  are  not  very  much  crowded 
by  company,  nor  filled  with  a  great  many  burning  lamps 
or  candles,  the  air  in  them  is  seldom  so  much  injured 
as  to  become  oppressive  or  unwholesome,  and  those 
who  inhabit  them  show  by  their  ruddy  countenances,  as 


490  Of  Chimney  Fireplaces. 

well  as  by  every  other  sign  of  perfect  health,  that  they 
suffer  no  inconvenience  whatever  from  their  closeness. 
There  is  frequently,  it  is  true,  an  oppressiveness  in  the 
air  of  a  room  heated  by  a  German  stove,  of  which  those 
who  are  not  so  much  accustomed  to  living  in  those 
rooms  seldom  fail  to  complain,  and  indeed  with  much 
reason ;  but  this  oppressiveness  does  not  arise  from  the 
air  of  the  room  being  injured  by  the  respiration  and 
perspiration  of  those  who  inhabit  it ;  it  arises  from  a 
very  different  cause,  —  from  a  fault  in  the  construction 
of  German  stoves  in  general,  but  which  may  be  easily 
and  most  completely  remedied,  as  I  shall  show  more 
fully  in  another  place.  In  the  mean  time,  I  would  just 
observe  here  with  regard  to  these  stoves,  that  as  they 
are  often  made  of  iron,  and  as  this  metal  is  a  very  good 
conductor  of  heat,  some  part  of  the  stove  in  contact 
with  the  air  of  the  room  becomes  so  hot  as  to  calcine  or 
rather  to  roast  the  dust  which  lights  upon  it ;  which  never 
can  fail  to  produce  a  very  disagreeable  effect  on  the  air 
of  the  room.  And  even  when  the  stove  is  constructed 
of  pantiles  or  pottery-ware,  if  any  part  of  it  in  contact 
with  the  air  of  the  room  is  suffered  to  become  very  hot, 
which  seldom  fails  to  be  the  case  in  German  stoves  con- 
structed on  the  common  principles,  nearly  the  same 
effects  will  be  found  to  be  produced  on  the  air  as  when 
the  stove  is  made  of  iron,  as  I  have  very  frequently  had 
occasion  to  observe. 

Though  a  room  be  closed  in  the  most  perfect  manner 
possible,  yet,  as  the  quantity  of  air  injured  and  rendered 
unfit  for  further  use  by  the  respiration  of  two  or  three 
persons  in  a  few  hours  is  very  small  compared  to  the 
immense  volume  of  air  which  a  room  of  a  moderate 
size  contains ;  and  as  a  large  quantity  of  fresh  air 


Of  Chimney  Fireplaces.  491 

always  enters  the  room,  and  an  equal  quantity  of  the 
warm  air  of  the  room  is  driven  out  of  it  every  time  the 
door  is  opened,  there  is  much  less  danger  of  the  air  of 
a  room  becoming  unwholesome  for  the  want  of  ventila- 
tion than  has  been  generally  imagined ;  particularly  in 
cold  weather,  when  all  the  different  causes  which  con- 
spire to  change  the  air  of  warmed  rooms  act  with  in- 
creased power  and  effect. 

Those  who  have  any  doubts  respecting  the  very  great 
change  of  air  or  ventilation  which  takes  place  each  time 
the  door  of  a  warm  room  is  opened  in  cold  weather, 
need  only  set  the  door  of  such  a  room  wide  open  for  a 
moment,  and  hold  two  lighted  candles  in  the  doorway, 
one  near  the  top  of  the  door  and  the  other  near  the  bot- 
tom of  it :  the  violence  with  which  the  flame  of  that  above 
will  be  driven  outwards,  and  that  below  inwards,  by  the 
two  strong  currents  of  air  which,  passing  in  opposite 
directions,  rush  in  and  out  of  the  room  at  the  same  time, 
will  be  convinced  that  the  change  of  air  which  actually 
takes  place  must  be  very  considerable  indeed  ;  and  these 
currents  will  be  stronger,  and  consequently  the  change 
of  air  greater,  in  proportion  as  the  difference  is  greater 
between  the  temperatures  of  the  air  within  the  room  and 
of  that  without.  I  have  been  more  particular  upon  this 
subject,  — the  ventilation  of  warmed  rooms  which  are 
constantly  inhabited, — as  I  know  that  people  in  gen- 
eral in  this  country  have  great  apprehensions  of  the  bad 
consequences  to  health  of  living  in  rooms  in  which  there 
is  not  a  continual  influx  of  cold  air  from  without.  I 
am  as  much  an  advocate  for  a  free  circulation  of  air  as 
anybody,  and  always  sleep  in  a  bed  without  curtains  on 
that  account;  but  I  am  much  inclined  to  think,  that  the 
currents  of  cold  air  which  never  fail  to  be  produced  in 


49 2  Of  CJiimney  Fireplaces. 

rooms  heated  by  fireplaces  constructed  upon  the  com- 
mon principle,  — those  partial  heats  on  one  side  of  the 
body,  and  cold  blasts  on  the  other,  so  often  felt  in 
houses  in  this  country,  — are  infinitely  more  detrimental 
to  health  than  the  supposed  closeness  of  the  air  in  a 
room  warmed  more  equally,  and  by  a  smaller  fire. 

All  these  advantages,  attending  the  introduction  of 
the  improvements  in  fireplaces  here  recommended,  are 
certainly  important,  and  I  do  not  know  that  they  are 
counterbalanced  by  any  one  disadvantage  whatsoever. 
The  only  complaint  that  I  have  ever  heard  made  against 
them  was  that  they  made  the  rooms  too  warm  ;  but  the 
remedy  to  this  evil  is  so  perfectly  simple  and  obvious, 
that  I  should  be  almost  afraid  to  mention  it,  lest  it 
might  be  considered  as  an  insult  to  the  understanding 
of  the  person  to  whom  such  information  should  be 
given ;  for  nothing  surely  can  be  conceived  more  per- 
fectly ridiculous  than  the  embarrassment  of  a  person 
on  account  of  the  too  great  heat  of  his  room,  when  it 
is  in  his  power  to  diminish  at  pleasure  the  fire  by  which 
it  is  warmed ;  and  yet,  strange  as  it  may  appear,  this 
has  sometimes  happened ! 

Before  I  proceed  to  give  directions  for  the  construc- 
tion of  fireplaces,  it  will  be  proper  to  examine  more 
carefully  the  fireplaces  now  in  common  use;  to  point 
out  their  faults  ;  and  to  establish  the  principles  upon 
which  fireplaces  ought  to  be  constructed. 

The  great  fault  of  all  the  open  fireplaces,  or  chimneys, 
for  burning  wood  or  coals  in  an  open  fire,  now  in  com- 
mon use,  is,  that  they  are  much  too  large ;  or,  rather,  it 
is  the  throat  of  the  chimney^  or  the  lower  part  of  its  open 
canal,  in  the  neighborhood  of  the  mantle  and  immedi- 
ately over  the  fire,  which  is  too  large.  This  opening 


Of  Chimney  Fireplaces.  493 

has  hitherto  been  left  larger  than  otherwise  it  probably 
would  have  been  made,  in  order  to  give  a  passage  to  the 
chimney-sweeper;  but  I  shall  show  hereafter  how  a 
passage  for  the  chimney-sweeper  may  be  contrived  with- 
out leaving  the  throat  of  the  chimney  of  such  enor- 
mous dimensions  as  to  swallow  up  and  devour  all  the 
warm  air  of  the  room,  instead  of  merely  giving  a  pas- 
sage to  the  smoke  and  heated  vapour  which  rise  from 
the  fire,  for  which  last  purpose  alone  it  ought  to  be 
destined. 

Were  it  my  intention  to  treat  my  subject  in  a  formal 
scientific  manner,  it  would  doubtless  be  proper,  and 
even  necessary,  to  begin  by  explaining  in  the  fullest 
manner,  and  upon  the  principles  founded  on  the  laws 
of  nature,  relative  to  the  motions  of  elastic  fluids,  as 
far  as  they  have  been  discovered  and  demonstrated,  the 
causes  of  the  ascent  of  smoke;  and  also  to  explain  and 
illustrate  upon  the  same  principles,  and  even  to  measure 
or  estimate  by  calculations,  the  precise  effects  of  all 
those  mechanical  aids  which  may  be  proposed  for  assist- 
ing it  in  its  ascent,  or  rather  for  removing  those  ob- 
stacles which  hinder  its  motion  upwards ;  but  as  it  is 
my  wish  rather  to  write  a  useful  practical  treatise  than  a 
learned  dissertation, —  being  more  desirous  to  contribute 
in  diffusing  useful  knowledge  by  which  the  comforts 
and  enjoyments  of  mankind  may  be  increased,  than  to 
acquire  the  reputation  of  a  philosopher  among  learned 
men,  —  I  shall  endeavour  to  write  in  such  a  manner  as  to 
be  easily  understood  by  those  who  are  most  likely  to  profit 
by  the  information  I  have  to  communicate^  and  consequently 
most  likely  to  assist  in  bringing  into  general  use  the 
improvements  I  recommend.  This  being  premised,  I 
shall  proceed,  without  any  further  preface  or  introduc- 


494  Q/  Chimney  Fireplaces. 

tion,  to  the  investigation  of  the  subject  I  have  under- 
taken to  treat. 

As  the  immoderate  size  of  the  throats  of  chimneys  is 
the  great  fault  of  their  construction,  it  is  this  fault 
which  ought  always  to  be  first  attended  to  in  every 
attempt  which  is  made  to  improve  them  ;  for  however 
perfect  the  construction  of  a  fireplace  may  be  in  other 
respects,  if  the  opening  left  for  the  passage  of  the 
smoke  is  larger  than  is  necessary  for  that  purpose,  noth- 
ing can  prevent  the  warm  air  of  the  room  from  escaping 
through  it ;  and  whenever  this  happens,  there  is  not 
only  an  unnecessary  loss  of  heat,  but  the  warm  air  which 
leaves  the  room  to  go  up  the  chimney  being  replaced  by 
cold  air  from  without,  the  draughts  of  cold  air,  so  often 
mentioned,  cannot  fail  to  be  produced  in  the  room, 
to  the  great  annoyance  of  those  who  inhabit  it.  But 
although  both  these  evils  may  be  effectually  remedied 
by  reducing  the  throat  of  the  chimney  to  a  proper  size, 
yet  in  doing  this  several  precautions  will  be  necessary. 
And  first  of  all,  the  throat  of  the  chimney  should  be  in 
its  proper  place :  that  is  to  say,  in  that  place  in  which  it 
ought  to  be,  in  order  that  the  ascent  of  the  smoke  may 
be  most  facilitated ;  for  every  means  which  can  be  em- 
ployed for  facilitating  the  ascent  of  the  smoke  in  the 
chimney  must  naturally  tend  to  prevent  the  chimney 
from  smoking;  now  as  the  smoke  and  hot  vapour  which 
rise  from  a  fire  naturally  tend  upwards,  the  proper  place 
for  the  throat  of  the  chimney  is  evidently  perpendicu- 
larly over  the  fire. 

But  there  is  another  circumstance  to  be  attended  to 
in  determining  the  proper  place  for  the  throat  of  a 
chimney,  and  that  is  to  ascertain  its  distance  from  the 
fire,  or  how  far  above  the  burning  fuel  it  ought  to  be 


Of  Chimney  Fireplaces.  495 

placed.  In  determining  this  point,  there  are  many 
things  to  be  considered,  and  several  advantages  and  dis- 
advantages to  be  weighed  and  balanced. 

As  the  smoke  and  vapour  which  ascend  from  burning 
fuel  rise  in  consequence  of  their  being  rarefied  by  heat, 
and  made  lighter  than  the  air  of  the  surrounding  at- 
mosphere ;  and  as  the  degree  of  their  rarefaction,  and 
consequently  their  tendency  to  rise,  is  in  proportion  to 
the  intensity  of  their  heat ;  and  further,  as  they  are 
hotter  near  the  fire  than  at  a  greater  distance  from  it,  it  is 
clear  that  the  nearer  the  throat  of  a  chimney  is  to  the 
fire,  the  stronger  will  be  what  is  commonly  called  its 
draught^  and  the  less  danger  there  will  be  of  its  smoking. 
But  on  the  other  hand,  when  the  draught  of  a  chimney 
is  very  strong,  and  particularly  when  this  strong  draught 
is  occasioned  by  the  throat  of  the  chimney  being  very 
near  the  fire,  it  may  so  happen  that  the  draught  of  air 
into  the  fire  may  become  so  strong  as  to  cause  the  fuel 
to  be  consumed  too  rapidly.  There  are  likewise  several 
other  inconveniences  which  would  attend  the  placing  of 
the  throat  of  a  chimney  very  near  the  burning  fuel. 

In  introducing  the  improvements  proposed,  in  chim- 
neys already  built,  there  can  be  no  question  in  regard  to 
the  height  of  the  throat  of  the  chimney,^for  its  place 
will  be  determined  by  the  height  of  the  mantle.  It  can 
hardly  be  made  lower  than  the  mantle;  and  it  ought 
always  to  be  brought  down  as  nearly  upon  the  level  with 
the  bottom  of  it  as  possible.  If  the  chimney  is  apt  to 
smoke,  it  will  sometimes  be  necessary  either  to  lower 
the  mantle  or  to  diminish  the  height  of  the  opening  of 
the  fireplace,  by  throwing  over  a  flat  arch,  or  putting  in 
a  straight  piece  of  stone  from  one  side  of  it  to  the 
other,  or,  which  will  be  still  more,  simple  and  easy  in 


496  Of  Chimney  Fireplaces. 

practice,  building  a  wall  of  bricks,  supported  by  a  flat 
bar  of  iron,  immediately  under  the  mantle. 

Nothing  is  so  effectual  to  prevent  chimneys  from 
smoking  as  diminishing  the  opening  of  the  fireplace  in 
the  manner  here  described,  and  lowering  and  diminishing 
the  throat  of  the  chimney;  and  I  have  always  found, 
except  in  the  single  instance  already  mentioned,  that  a 
perfect  cure  may  be  effected  by  these  means  alone,  even  in 
the  most  desperate  cases.  It  is  true,  that  when  the  con- 
struction of  the  chimney  is  very  bad  indeed,  or  its  situ- 
ation very  unfavourable  to  the  ascent  of  the  smoke,  and 
especially  when  both  these  disadvantages  exist  at  the 
same  time,  it  may  sometimes  be  necessary  to  diminish 
the  opening  of  the  fireplace,  and  particularly  to  lower  it, 
and  also  to  lower  the  throat  of  the  chimney,  more  than 
might  be  wished ;  but  still  I  think  this  can  produce  no 
inconveniences  to  be  compared  with  that  greatest  of  all 
plagues,  a  smoking  chimney. 

The  position  of  the  throat  of  a  chimney  being  de- 
termined, the  next  points  to  be  ascertained  are  its  size 
and  form,  and  the  manner  in  which  it  ought  to  be  con- 
nected with  the  fireplace  below,  and  with  the  open  canal 
of  the  chimney  above. 

But  as  the.se  investigations  are  intimately  connected 
with  those  which  relate  to  the  form  proper  to  be  given  to 
the  fireplace  itself,  we  must  consider  them  all  together. 

That  these  inquiries  may  be  pursued  with  due  method, 
and  that  the  conclusions  drawn  from  them  may  be  clear 
and  satisfactory,  it  will  be  necessary  to  consider,  first, 
what  the  objects  are  which  ought  principally  to  be  had 
in  view  in  the  construction  of  a  fireplace;  and  secondly, 
to  see  how  these  objects  can  best  be  attained. 

Now  the  design  of  a  chimney  fire  being  simply  to 


Of  Chimney  Fireplaces.  497 

warm  a  room,  it  is  necessary,  first  of  all,  to  contrive 
matters  so  that  the  room  shall  be  actually  warmed ; 
secondly,  that  it  be  warmed  with  the  smallest  expense 
of  fuel  possible  ;  and,  thirdly,  that,  in  warming  it,  the 
air  of  the  room  be  preserved  perfectly  pure  and  fit  for 
respiration,  and  free  from  smoke  and  all  disagreeable 
smells. 

In  order  to  take  measures  with  certainty  for  warming 
a  room  by  means  of  an  open  chimney  fire,  it  will  be 
necessary  to  consider  how,  or  in  what  manner,  such  a  fire 
communicates  heat  to  a  room.  This  question  may  per- 
haps, at  the  first  view  of  it,  appear  to  be  superfluous 
and  trifling,  but  a  more  careful  examination  of  the 
matter  will  show  it  to  be  highly  deserving  of  the  most 
attentive  investigation. 

To  determine  in  what  manner  a  room  is  heated  by  an 
open  chimney  fire,  it  will  be  necessary,  first  of  all,  to 
find  out  under  what  form  the  heat  generated  in  the  com- 
bustion of  the  fuel  exists,  and  then  to  see  how  it  is 
communicated  to  those  bodies  which  are  heated  by  it. 

In  regard  to  the  first  of  these  subjects  of  inquiry,  it 
is  quite  certain  that  the  heat  which  is  generated  in  the 
combustion  of  the  fuel  exists  under  two  perfectly  dis- 
tinct and  very  different  forms.  One  part  of  it  is  com- 
bined with  the  smoke,  vapour,  and  heated  air,  which  rise 
from  the  burning  fuel,  and  goes  off  with  them  into  the 
upper  regions  of  the  atmosphere ;  while  the  other  part, 
which  appears  to  be  uncombined,  or,  as  some  ingenious 
philosophers  have  supposed,  combined  only  with  light, 
is  sent  off  from  the  fire  in  rays  in  all  possible  directions. 

With  respect  to  the  second  subject  of  inquiry, 
namely,  —  how  this  heat,  existing  under  these  two  differ- 
ent forms,  is  communicated  toother  bodies  ;  it  is  highly 

VOL.  n.  32 


49  8  Of  Chimney  Fireplaces. 

probable  that  the  combined  heat  can  only  be  communi- 
cated to  other  bodies  by  actual  contact  with  the  body  with 
which  it  is  combined ;  and  with  regard  to  the  rays  which 
are  sent  off  by  burning  fuel,  it  is  certain  that  they  com- 
municate or  generate  heat  only  when  and  where  they  are 
stopped  or  absorbed.  In  passing  through  air,  which  is 
transparent,  they  certainly  do  not  communicate  any  heat 
to  it;  and  it  seems  highly  probable  that  they  do  not 
communicate  heat  to  solid  bodies  by  which  they  are 
reflected. 

In  these  respects  they  seem  to  bear  a  great  resem- 
blance to  the  solar  rays.  But  n  order  not  to  distract 
the  attention  of  my  reader  or  carry  him  too  far  away 
from  the  subject  more  immediately  under  consideration, 
I  must  not  enter  too  deeply  into  these  inquiries  respect- 
ing the  nature  and  properties  of  what  has  been  called  radi- 
ant heat.  It  is  certainly  a  most  curious  subject  of  philo- 
sophical investigation,  but  more  time  would  be  required 
to  do  it  justice  than  we  now  have  to  spare.  We  must, 
therefore,  content  ourselves  with  such  a  partial  examina- 
tion of  it  as  will  be  sufficient  for  our  present  purpose. 

A  question  which  naturally  presents  itself  here  is, 
What  proportion  does  the  radiant  heat  bear  to  the  com- 
bined heat  ?  Though  that  point  has  not  yet  been  de- 
termined with  any  considerable  degree  of  precision,  it 
is,  however,  quite  certain,  that  the  quantity  of  heat 
which  goes  off  combined  with  the  smoke,  vapour,  and 
heated  air,  is  much  more  considerable,  perhaps  three  or 
four  times  greater,  at  least,  than  that  which  is  sent  off 
from  the  fire  in  rays.  And  yet,  small  as  the  quantity  is 
of  this  radiant  heat,  it  is  the  only  part  of  the  heat  gene- 
rated in  the  combustion  of  fuel  burned  in  an  open  fire- 
place, which  is  ever  employed,  or  which  can  ever  be  em- 
ployed, in  heating  a  room. 


Of  Chimney  Fireplaces.  499 

The  whole  of  the  combined  heat  escapes  by  the  chim- 
ney, and  is  totally  lost ;  and,  indeed,  no  part  of  it  could 
ever  be  brought  into  a  room  from  an  open  fireplace, 
without  bringing  along  with  it  the  smoke  with  which  it 
is  combined  ;  which,  of  course,  would  render  it  impos- 
sible for  the  room  to  be  inhabited.'  There  is,  however, 
one  method  by  which  combined  heat,  and  even  that 
which  arises  from  an  open  fireplace,  may  be  made  to 
assist  in  warming  a  room ;  and  that  is  by  making  it  pass 
through  something  analogous  to  a  German  stove,  placed 
in  the  chimney  above  the  fire.  But  of  this  contrivance 
I  shall  take  occasion  to  treat  more  fully  hereafter;  in 
the  mean  time  I  shall  continue  to  investigate  the  prop- 
erties of  open  chimney  fireplaces,  constructed  upon  the 
most  simple  principles,  such  as  are  now  in  common 
use ;  and  shall  endeavour  to  point  out  and  explain  all 
those  improvements  of  which  they  appear  to  me  to  be 
capable.  When  fuel  is  burned  in  fireplaces  upon  this 
simple  construction,  where  the  smoke  escapes  immedi- 
ately by  the  open  canal  of  the  chimney,  it  is  quite  evi- 
dent that  all  the  combined  heat  must  of  necessity  be 
lost ;  and  as  it  is  the  radiant  heat  alone  which  can  be 
employed  in  heating  a  room,  it  becomes  an  object  of 
much  importance  to  determine  how  the  greatest  quantity 
of  it  may  be  generated  in  the  combustion  of  the  fuel, 
and  how  the  greatest  proportion  possible  of  that  gene- 
rated may  be  brought  into  the  room. 

Now,  the  quantity  of  radiant  heat  generated  in  the 
combustion  of  a  given  quantity  of  any  kind  of  fuel 
depends  very  much  upon  the  management  of  the  fire, 
or  upon  the  manner  in  which  the  fuel  is  consumed. 
When  the  fire  burns  bright,  much  radiant  heat  will  be 
sent  off  from  it ;  but  when  it  is  smothered  up,  very  little 


500  Of  Chimney  Fireplaces. 

will  be  generated ;  and  indeed  very  little  combined 
heat,  that  can  be  employed  to  any  useful  purpose; 
most  of  the  heat  produced  will  be  immediately  expended 
in  giving  elasticity  to  a  thick  dense  vapour  or  smoke 
which  will  be  seen  rising  from  the  fire  ;  and  the  combus- 
tion being  very  incomplete,  a  great  part  of  the  inflam- 
mable matter  of  the  fuel  being  merely  rarefied  and 
driven  up  the  chimney  without  being  inflamed,  the  fuel 
will  be  wasted  to  little  purpose.  And  hence  it  appears 
of  how  much  importance  it  is,  whether  it  be  considered 
with  a  view  to  economy,  or  to  cleanliness,  comfort,  and 
elegance,  to  pay  due  attention  to  the  management  of  a 
chimney  fire. 

Nothing  can  be  more  perfectly  void  of  common- 
sense,  and  wasteful  and  slovenly  at  the  same  time,  than 
the  manner  in  which  chimney  fires,  and  particularly 
where  coals  are  burned,  are  commonly  managed  by  ser- 
vants. They  throw  on  a  load  of  coals  at  once,  through 
which  the  flame  is  hours  in  making  its  way  ;  and  fre- 
quently it  is  not  without  much  trouble  that  the  fire  is 
prevented  from  going  quite  out.  During  this  time,  no 
heat  is  communicated  to  the  room  ;  and  what  is  still 
worse,  the  throat  of  the  chimney,  being  occupied  merely 
by  a  heavy  dense  vapour  not  possessed  of  any  consider- 
able degree  of  heat,  and  consequently  not  having  much 
elasticity,  the  warm  air  of  the  room  finds  less  difficulty 
in  forcing  its  way  up  the  chimney  and  escaping,  than 
when  the  fire  burns  bright;  and  it  happens  not  unfre- 
quently,  especially  in  chimneys  and  fireplaces  ill  con- 
structed, that  this  current  of  warm  air  from  the  room, 
which  presses  into  the  chimney,  crossing  upon  the  cur- 
rent of  heavy  smoke  which  rises  slowly  from  the  fire, 
obstructs  it  in  its  ascent,  and  beats  it  back  into  the 


Of  Chim ney  Fireplaces.  50 1 

room  ;  hence  it  is  that  chimneys  so  often  smoke  when 
too  large  a  quantity  of  fresh  coals  is  put  upon  the  fire. 
So  many  coals  should  never  be  put  on  the  fire  at  once, 
as  to  prevent  the  free  passage  of  the  flame  between.  In 
short,  a  fire  should  never  be  smothered ;  and  when 
proper  attention  is  paid  to  the  quantity  of  coals  put  on, 
there  will  be  very  little  use  for  the  poker ;  and  this  cir- 
cumstance will  contribute  very  much  to  cleanliness  and 
to  the  preservation  of  furniture. 

Those  who  have  feeling  enough  to  be  made  miserable 
by  anything  careless,  slovenly,  and  wasteful,  which  hap- 
pens under  their  eyes,  who  know  what  comfort  is,  and 
consequently  are  worthy  of  the  enjoyments  of  a  clean 
hearth  and  cheerful  fire,  should  really  either  take  the 
trouble  themselves  to  manage  their  fires  (which,  indeed, 
would  rather  be  an  amusement  to  them  than  a  trouble), 
or  they  should  instruct  their  servants  to  manage  them 
better. 

But  to  return  to  the  subject  more  immediately  under 
consideration.  As  we  have  seen  what  is  necessary  to 
the  production  or  generation  of  radiant  heat,  it  remains 
to  determine  how  the  greatest  proportion  of  that  gene- 
rated and  sent  off  from  the  fire  in  all  directions  may  be 
made  to  enter  the  room,  and  assist  in  warming  it.  Now, 
as  the  rays  which  are  thrown  off  from  burning  fuel  have 
this  property  in  common  with  light,  that  they  generate 
heat  only  when  and  where  they  are  stopped  or  absorbed, 
and  also  in  being  capable  of  being  reflected  without  gene- 
rating heat  at  the  surfaces  of  various  bodies,  the  knowl- 
edge of  these  properties  will  enable  us  to  take  measures, 
with  the  utmost  certainty,  for  producing  the  effect  re- 
quired,—  that  is  to  say,  for  bringing  as  much  radiant 
heat  as  possible  into  the  room. 


502  Of  Chimney  Fireplaces. 

This  must  be  done,  first,  by  causing  as  many  as  pos- 
sible of  the  rays,  as  they  are  sent  off  from  the  fire  in 
straight  lines,  to  come  directly  into  the  room  ;  which  can 
only  be  effected  by  bringing  the  fire  as  far  forward  as 
possible,  and  leaving  the  opening  of  the  fireplace  as 
wide  and  as  high  as  can  be  done  without  inconvenience ; 
and  secondly,  by  making  the  sides  and  back  of  the  fire- 
place of  such  form,  and  constructing  them  of  such 
materials,  as  to  cause  the  direct  rays  from  the  fire,  which 
strike  against  them,  to  be  sent  into  the  room  by  reflection 
in  the  greatest  abundance. 

Now  it  will  be  found,  upon  examination,  that  the 
best  form  for  the  vertical  sides  of  a  fireplace,  or  the 
covings  (as  they  are  called),  is  that  of  an  upright  plane, 
making  an  angle  with  the  plane  of  the  back  of  the  fire- 
place of  about  135  degrees.  According  to  the  present 
construction  of  chimneys,  this  angle  is  90  degrees,  or 
forms  a  right  angle ;  but  as  in  this  case  the  two  sides  or 
covings  of  the  fireplace  (A  C,  B  D,  Plate  VIII.,  Fig.  i) 
are  parallel  to  each  other,  it  is  evident  that  they  are  very 
ill  contrived  for  throwing  into  the  room  by  reflection 
the  rays  from  the  fire  which  fall  on  them. 

To  have  a  clear  and  perfect  idea  of  the  alterations  I 
propose  in  the  forms  'of  fireplaces,  the  reader  need  only 
observe,  that,  whereas  the  backs  of  fireplaces,  as  they 
are  now  commonly  constructed,  are  as  wide  as  the  open- 
ing of  the  fireplace  in  front,  and  the  sides  of  it  are  of 
course  perpendicular  to  it  and  parallel  to  each  other,  —  in 
the  fireplaces  I  recommend,  the  back  (/'  k,  Plate  IX., 
Fig.  3)  is  only  about  one  third  of  the  width  of  the  open- 
ing of  the  fireplace  in  front  (a  b\  and  consequently  that 
the  two  sides  or  covings  of  the  fireplace  (a  i  and  b  k\ 
instead  of  being  perpendicular  to  the  back,  are  inclined 


Of  Chimney  Fireplaces.  503 

to  it  at  an  angle  of  about  135  degrees;  and  in  conse- 
quence of  this  position,  instead  of  being  parallel  to  each 
other,  each  of  them  presents  an  oblique  front  towards 
the  opening  of  the  chimney,  by  means  of  which  the 
rays  which  they  reflect  are  thrown  into  the  room.  A 
bare  inspection  of  the  annexed  drawings  (Plate  VIII., 
Fig.  i,  and  Plate  IX.,  Fig.  3)  will  render  this  matter 
perfectly  clear  and  intelligible. 

In  regard  to  the  materials  which  it  will  be  most  ad- 
vantageous to  employ  in  the  construction  of  fireplaces, 
so  much  light  has,  I  flatter  myself,  already  been  thrown 
on  the  subject  we  are  investigating,  and  the  principles 
adopted  have  been  established  on  such  clear  and  obvious 
facts,  that  no  great  difficulty  will  attend  the  determina- 
tion of  that  point.  As  the  object  in  view  is  to  bring 
radiant  heat  into  the  room,  it  is  clear  that  that  material 
is  best  for  the  construction  of  a  fireplace,  which  reflects 
the  most,  o'r  which  absorbs  the  least  of  it ;  for  that  heat 
which  is  absorbed  cannot  be  reflected.  Now,  as  bodies 
which  absorb  radiant  heat  are  necessarily  heated  in  con- 
sequence of  that  absorption,  to  discover  which  of  the 
various  materials  that  can  be  employed  for  constructing 
fireplaces  are  best  adapted  for  that  purpose,  we  have 
only  to  find  out  by  an  experiment,  very  easy  to  be 
made,  what  bodies  acquire  least  heat  when  exposed  to 
the  direct  rays  of  a  clear  fire ;  for  those  which  are  least 
heated  evidently  absorb  the  least,  and  consequently 
reflect  the  most  radiant  heat.  And  hence  it  appears 
that  iron,  and,  in  general,  metals  of  all  kinds,  which  are 
well  known  to  grow  'very  hot  when  exposed  to  the  rays 
projected  by  burning  fuel,  are  to  be  reckoned  among  the 
'very  worst  materials  that  it  is  possible  to  employ  in  the 
construction  of  fireplaces. 


504  Of  Chimney  Fireplaces. 

The  best  materials  I  have  hitherto  been  able  to  dis- 
cover are  fire-stone,  and  common  bricks  and  mortar. 
Both  these  materials  are,  fortunately,  very  cheap;  and 
as  to  their  comparative  merits,  I  hardly  know  to  which 
of  them  the  preference  ought  to  be  given. 

When  bricks  are  used,  they  should  be  covered  with  a 
thin  coating  of  plaster,  which,  when  it  is  become  per- 
fectly dry,  should  be  whitewashed.  The  fire-stone 
should  likewise  be  whitewashed,  when  that  is  used ; 
and  every  part  of  the  fireplace,  which  is  not  exposed  to 
being  soiled  and  made  black  by  the  smoke,  should  be 
kept  as  white  and  clean  as  possible.  As  white  reflects 
more  heat,  as  well  as  more  light,  than  any  other  colour, 
it  ought  always  to  be  preferred  for  the  inside  of  a  chim- 
ney fireplace,  and  black,  which  reflects  neither  light  nor 
heat,  should  be  most  avoided. 

I  am  well  aware  how  much  the  opinion  I  have  here 
ventured  to  give,  respecting  the  unfitness  of  iron  and 
other  metals  to  be  employed  in  the  construction  of  open 
fireplaces,  differs  from  the  opinion  generally  received 
upon  that  subject ;  and  I  even  know  that  the  very 
reason,  which,  according  to  my  ideas  of  the  matter,  ren- 
ders them  totally  unfit  for  the  purpose,  is  commonly  as- 
signed for  making  use  of  them  ;  namely, — that  they  soon 
grow  very  hot.  But  I  would  beg  leave  to  ask  what  ad- 
vantage is  derived  from  heating  them  ? 

I  have  shown  the  disadvantage  of  it;  namely, —  that  the 
quantity  of  radiant  heat  thrown  into  the  room  is  dimin- 
ished ;  and  it  is  easy  to  show  that  almost  the  whole  of 
that  absorbed  by  the  metal  is  ultimately  carried  up  the 
chimney  by  the  air,  which,  coming  into  contact  with 
this  hot  metal,  is  heated  and  rarefied  by  it,  and,  forcing 
its  way  upwards,  goes  off  with  the  smoke ;  and  as  no 


Of  Chimney  Fireplaces.  505 

current  of  air  ever  sets  from  any  part  of  the  opening  of 
a  fireplace  into  the  room,  it  is  impossible  to  conceive 
how  the  heat  existing  in  the  metal  composing  any  part 
of  the  apparatus  of  the  fireplace,  and  situated  within  its 
cavity,  can  come,  or  be  brought,  into  the  room. 

This  difficulty  may  be  in  part  removed,  by  supposing, 
what  indeed  seems  to  be  true  in  a  certain  degree,  that 
the  heated  metal  sends  off  in  rays  the  heat  it  acquires 
from  the  fire,  even  when  it  is  not  heated  red-hot ;  but 
still,  as  it  never  can  be  admitted  that  the  heat  absorbed 
by  the  metal,  and  afterwards  thrown  off  by  it  in  rays,  is 
increased  by  this  operation,  nothing  can  be  gained  by  it ; 
and  as  much  must  necessarily  be  lost  in  consequence  of 
the  great  quantity  of  heat  communicated  by  the  hot 
metal  to  the  air  in  contact  with  it,  which,  as  has  already 
been  shown,  always  makes  its  way  up  the  chimney,  and 
flies  off  into  the  atmosphere,  the  loss  of  heat  attending 
the  use  of  it  is  too  evident  to  require  being  further  in- 
sisted on. 

There  is,  however,  in  chimney  fireplaces  destined  for 
burning  coals,  one  essential  part,  the  grate,  which  cannot 
well  be  made  of  anything  else  but  iron  ;  but  there  is  no 
necessity  whatever  for  that  immense  quantity  of  iron 
which  surrounds  grates  as  they  are  now  commonly  con- 
structed and  fitted  up,  and  which  not  only  renders  them 
very  expensive,  but  injures  very  essentially  the  fireplace. 
If  it  should  be  necessary  to  diminish  the  opening  of 
a  large  chimney  in  order  to  prevent  its  smoking,  it 
is  much  more  simple,  economical,  and  better  in  all 
respects,  to  do  this  with  marble,  fire-stone,  or  even  with 
bricks  and  mortar,  than  to  make  use  of  iron,  which,  as 
has  already  been  shown,  is  the  very  worst  material  that 
can  possibly  be  employed  for  that  purpose ;  and  as 


5o5  Of  Chimney  Fireplaces. 

to  registers,  they  not  only  are  quite  unnecessary  where 
the  throat  of  a  chimney  is  properly  constructed,  and  of 
proper  dimensions,  but  in  that  case  would  do  much 
harm.  If  they  act  at  all,  it  must  be  by  opposing  their 
flat  surfaces  to  the  current  of  rising  smoke  in  a  manner 
which  cannot  fail  to  embarrass  and  impede  its  motion. 
But  wre  have  shown  that  the  passage  of  the  smoke 
through  the  throat  of  a  chimney  ought  to  be  facilitated 
as  much  as  possible,  in  order  that  it  may  be  enabled  to 
pass  by  a  small  aperture. 

Register  stoves  have  often  been  found  to  be  of  use ; 
but  it  is  because,  the  great  fault  of  all  fireplaces  con- 
structed upon  the  common  principles  being  the  enor- 
mous dimensions  of  the  throat  of  the  chimney,  this 
fault  has  been  in  some  measure  corrected  by  them ;  but 
I  will  venture  to  affirm  that  there  never  was  a  fireplace 
so  corrected  that  would  not  have  been  much  more  im- 
proved, and  with  infinitely  less  expense,  by  the  altera- 
tions here  recommended,  and  which  will  be  more  par- 
ticularly explained  in  the  next  chapter. 


CHAPTER    II. 

Practical  Directions  designed  for  the  Use  of  Workmen,  show- 
ing how  they  are  to  proceed  in  making  the  Alterations 
necessary  to  improve  Chimney  Fireplaces,  and  effectually  to 
cure  smoking  Chimneys. 

ALL  chimney  fireplaces,  without  exception,  whether 
they  are  designed  for  burning  wood  or  coals,  and 
even  those  which  do  not  smoke,  as  well  as  those  which 
do,  may  be  greatly  improved  by  making  the  alterations 


Of  Chimney  Fireplaces.  507 

in  them  here  recommended ;  for  it  is  by  no  means 
merely  to  prevent  chimneys  from  smoking  that  these  im- 
provements are  recommended,  but  it  is  also  to  make 
them  better  in  all  other  respects  as  fireplaces ;  and  when 
the  alterations  proposed  are  properly  executed,  which 
may  very  easily  be  done  with  the  assistance  of  the  fol- 
lowing plain  and  simple  directions,  the  chimneys  will 
never  fail  to  answer,  I  will  venturet  to  say,  even  beyond 
expectation.  The  room  will  be  heated  much  more 
equally  and  more  pleasantly  with  less  than  half  the  fuel 
used  before ;  the  fire  will  be  more  cheerful  and  more  agree- 
able, and  the  general  appearance  of  the  fireplace  more 
neat  and  elegant ;  and  the  chimney  will  never  smoke. 

The  advantages  which  are  derived  from  mechanical 
inventions  and  contrivances  are,  I  know,  frequently 
accompanied  by  disadvantages  which  it  is  not  always 
possible  to  avoid ;  but  in  the  case  in  question,  I  can  say 
with  truth,  that  I  know  of  no  disadvantage  whatever 
that  attends  the  fireplaces  constructed  upon  the  prin- 
ciples here  recommended.  But  to  proceed  in  giving 
directions  for  the  construction  of  these  fireplaces. 

That  what  I  have  to  offer  on  this  subject  may  be  the 
more  easily  understood,  it  will  be  proper  to  begin  by 
explaining  the  precise  meaning  of  all  those  technical 
words  and  expressions  which  I  may  find  it  necessary  or 
convenient  to  use. 

By  the  throat  of  a  chimney,  I  mean  the  lower  ex- 
tremity of  its  canal,  where  it  unites  with  the  upper  part 
of  its  open  fireplace.  This  throat  is  commonly  found 
about  a  foot  above  the  level  of  the  lower  part  of  the 
mantle,  and  it  is  sometimes  contracted  to  a  smaller  size 
than  the  rest  of  the  canal  of  the  chimney,  and  some- 
times not. 


508  Of  Chimney  Fireplaces. 

Plate  X.,  Fig.  5,  shows  the  section  of  a  chimney  on 
the  common  construction,  in  which  d  e  is  the  throat. 

Fig.  6  shows  the  section  of  the  same  chimney 
altered  and  improved,  in  which  di  is  the  reduced  throat. 

The  breast  of  a  chimney  is  that  part  of  it  which  is 
immediately  behind  the  mantle.  It  is  the  wall  which 
forms  the  entrance  from  below,  into  the  throat  of  the 
chimney  in  front,  or  towards  the  room.  It  is  opposite 
to  the  upper  extremity  of  the  back  of  the  open  fireplace, 
and  parallel  to  it ;  in  short,  it  may  be  said  to  be  the  back 
part  of  the  mantle  itself.  In  the  figures  5  and  6,  it  is 
marked  by  the  letter  d.  The  width  of  the  throat  of  the 
chimney  (d  e,  Fig.  5,  and  d  iy  Fig.  6)  is  taken  from  the 
breast  of  the  chimney  to  the  back,  and  its  length  is  taken 
at  right  angles  to  its  width,  or  in  a  line  parallel  to  the 
mantle  (a,  Figs.  5  and  6). 

Before  I  proceed  to  give  particular  directions  respect- 
ing the  exact  forms  and  dimensions  of  the  different 
parts  of  a  fireplace,  it  may  be  useful  to  make  such 
general  and  practical  observations  upon  the  subject  as 
can  be  clearly  understood  without  the  assistance  of 
drawings ;  for  the  more  complete  the  knowledge  of 
any  subject  is,  which  can  be  acquired  without  drawings, 
the  more  easy  will  it  be  to  understand  the  drawings  when 
it  becomes  necessary  to  have  recourse  to  them. 

The  bringing  forward  of  the  fire  into  the  room, 
or  rather  bringing  it  nearer  to  the  front  of  the  opening 
of  the  fireplace,  and  the  diminishing  of  the  throat  of 
the  chimney,  being  two  objects  principally  had  in  view 
in  the  alterations  in  fireplaces  here  recommended,  it  is 
evident  that  both  these  may  be  attained,  merely  by  bring- 
ing forward  the  back  of  the  chimney.  The  only  ques- 
tion therefore  is,  how  far  it  should  be  brought  forward. 


Of  Chimney  Fireplaces.  509 

The  answer  is  short,  and  easy  to  be  understood,  —  bring 
it  forward  as  far  as  possible,  without  diminishing  too 
much  the  passage  which  must  be  left  for  the  smoke. 
Now  as  this  passage,  which,  in  its  narrowest  part,  I 
have  called  the  throat  of  the  chimney^  ought,  for  reasons 
which  are  fully  explained  in  the  foregoing  chapter,  to  be 
immediately,  or  perpendicularly,  over  the  fire,  it  is  evi- 
dent that  the  back  of  the  chimney  must  always  be  built 
perfectly  upright.  To  determine  therefore  the  place  for 
the  new  back,  or  how  far  precisely  it  ought  to  be 
brought  forward,  nothing  more  is  necessary  than  to  as- 
certain how  wide  the  throat  of  the  chimney  ought  to  be 
left,  or  what  space  must  be  left  between  the  top  of  the 
breast  of  the  chimney,  where  the  upright  canal  of  the 
chimney  begins,  and  the  new  back  of  the  fireplace  carried 
up  perpendicularly  to  that  height. 

In  the  course  of  my  numerous  experiments  upon 
chimneys,  I  have  taken  much  pains  to  determine  the 
width  proper  to  be  given  to  this  passage,  and  I  have 
found,  that,  when  the  back  of  the  fireplace  is  of  a 
proper  width,  the  best  width  for  the  throat  of  a 
chimney,  when  the  chimney  and  the  fireplace  are  at  the 
usual  form  and  size,  is  four  inches.  Three  inches  might 
sometimes  answer,  especially  where  the  fireplace  is  very 
small,  and  the  chimney  good,  and  well  situated;  but  as 
it  is  always  of  much  importance  to  prevent  those  acci- 
dental puffs  of  smoke  which  are  sometimes  thrown  into 
rooms  by  the  carelessness  of  servants  in  putting  on  sud- 
denly too  many  coals  at  once  upon  the  fire,  and  as  I 
found  these  accidents  sometimes  happened  when  the 
throats  of  chimneys  were  made  very  narrow,  I  found 
that,  upon  the  whole,  all  circumstances  being  well  con- 
sidered, and  advantages  and  disadvantages  compared 


5 1  o  Of  Chimney  Fireplaces. 

and  balanced,  four  inches  is  the  best  width  that  can  be 
given  to  the  throat  of  a  chimney ;  and  this,  whether  the 
fireplace  be  destined  to  burn  wood,  coals,  turf,  or  any 
other  fuel  commonly  used  for  heating  rooms  by  an  open 
fire. 

In  fireplaces  destined  for  heating  very  large  halls,  and 
where  very  great  fires  are  kept  up,  the  throat  of  the 
chimney,  may,  if  it  should  be  thought  necessary,  be 
made  four  inches  and  an  half,  or  five  inches  wide ;  but  I 
have  frequently  made  fireplaces  for  halls,  which  have 
answered  perfectly  well,  where  the  throats  of  the  chimneys 
have  not  been  wider  than  four  inches. 

It  may  perhaps  appear  extraordinary,  upon  the  first 
view  of  the  matter,  that  fireplaces  of  such  different  sizes 
should  all  require  the  throat  of  the  chimney  to  be  of 
the  same  width ;  but  when  it  is  considered  that  the 
capacity  of  the  throat  of  a  chimney  does  not  depend  on 
its  width  alone,  but  on  its  width  and  length  taken 
together,  and  that  in  large  fireplaces,  the  width  of  the 
back,  and  consequently  the  length  of  the  throat  of  the 
chimney,  is  greater  than  in  those  which  are  smaller,  this 
difficulty  vanishes. 

And  this  leads  us  to  consider  another  important  point 
respecting  open  fireplaces,  and  that  is,  the  width  which 
it  will,  in  each  case,  be  proper  to  give  to  the  back.  In 
fireplaces  as  they  are  now  commonly  constructed,  the 
back  is  of  equal  width  with  the  opening  of  the  fireplace 
in  front ;  but  this  construction  is  faulty  on  two  accounts. 
First,  in  a  fireplace  so  constructed,  the  sides  of  the 
fireplace — or  covings,  as  they  are  called  —  are  parallel  to 
each  other,  and  consequently  ill  contrived  to  throw  out 
into  the  room  the  heat  they  receive  from  the  fire  in  the 
form  of  rays  ;  and  secondly,  the  large  open  corners, 


Of  Chimney  Fireplaces.  5 1 1 

which  are  formed  by  making  the  back  as  wide  as  the 
opening  of  the  fireplace  in  front,  occasion  eddies  of  wind 
which  frequently  disturb  the  fire,  and  embarrass  the 
smoke  in  its  ascent  in  such  a  manner  as  often  to  bring 
it  into  the  room.  Both  these  defects  may  be  entirely 
remedied  by  diminishing  the  width  of  the  back  of  the 
fireplace.  The  width  which,  in  most  cases,  it  will  be 
best  to  give  it  is  one  third  of  the  width  of  the  opening 
of  the  fireplace  in  front.  But  it  is  not  absolutely  neces- 
sary to  conform  rigorously  to  this  decision,  nor  will  it 
always  be  possible.  It  will  frequently  happen  that  the 
back  of  a  chimney  must  be  made  wider  than,  according 
to  the  rule  here  given,  it  ought  to  be.  This  may  be 
either  to  accommodate  the  fireplace  to  a  stove,  which, 
being  already  on  hand,  must,  to  avoid  the  expense  of 
purchasing  a  new  one,  be  employed ;  or  for  other 
reasons ;  and  any  small  deviation  from  the  general  rule 
will  be  attended  with  no  considerable  inconvenience.  It 
will  always  be  best,  however,  to  conform  to  it  as  far  as 
circumstances  will  allow. 

Where  a  chimney  is  designed  for  warming  a  room  of 
a  middling  size,  and  where  the  thickness  of  the  wall  of 
the  chimney  in  front,  measured  from  the  front  of  the 
mantle  to  the  breast  of  the  chimney,  is  nine  inches,  I 
should  set  off  four  inches  more  for  the  width  of  the 
throat  of  the  chimney,  which,  supposing  the  back  of  the 
chimney  to  be  built  upright,  as  it  always  ought  to  be, 
will  give  thirteen  inches  for  the  depth  of  the  fireplace, 
measured  upon  the  hearth  from  the  opening  of  the  fire- 
place in  front  to  the  back.  In  this  case,  thirteen  inches 
would  be  a  good  size  for  the  width  of  the  back;  and 
three  times  thirteen  inches,  or  thirty-nine  inches,  for  the 
width  of  the  opening  of  the  fireplace  in  front ;  and  the 


512  Of  Chimney  Fireplaces. 

angle  made  by  the  back  of  the  fireplace  and  the  sides 
of  it,  or  covings,  would  be  just  135  degrees,  which  is 
the  best  position  they  can  have  for  throwing  heat  into 
the  room. 

But  I  will  suppose  that  in  altering  such  a  chimney  it 
is  found  necessary,  in  order  to  accommodate  the  fire- 
place to  a  grate  or  stove  already  on  hand,  to  make  the 
fireplace  sixteen  inches  wide.  In  that  case,  I  should 
merely  increase  the  width  of  the  back  to  the  dimensions 
required,  without  altering  the  depth  of  the  chimney  or 
increasing  the  width  of  the  opening  of  the  chimney  in 
front.  The  covings,  it  is  true,  would  be  somewhat 
reduced  in  their  width  by  this  alteration  ;  and  their 
position  with  respect  to  the  plane  of  the  back  of  the 
chimney  would  be  a  little  changed;  but  these  alterations 
would  produce  no  bad  effects  of  any  considerable  conse- 
quence, and  would  be  much  less  likely  to  injure  the  fire- 
place, than  an  attempt  to  bring  the  proportions  of  its 
parts  nearer  to  the  standard,  by  increasing  the  depth  of 
the  chimney,  and  the  width  of  its  opening  in  front ;  or 
than  an  attempt  to  preserve  that  particular  obliquity  of 
the  covings  which  is  recommended  as  the  best  (135 
degrees),  by  increasing  the  width  of  the  opening  of  the 
fireplace,  without  increasing  its  depth. 

In  order  to  illustrate  this  subject  more  fully,  we  will 
suppose  one  case  more.  We  will  suppose  that  in 
the  chimney  which  is  to  be  altered,  the  width  of  the  fire- 
place in  front  is  either  wider  or  narrower  than  it  ought 
to  be,  in  order  that  the  different  parts  of  the  fireplace, 
after  it  is  altered,  may  be  of  the  proper  dimensions.  In 
this  case,  I  should  determine  the  depth  of  the  fireplace, 
and  the  width  of  the  back  of  it,  without  any  regard  to  the 
width  of  the  opening  of  the  fireplace  in  front ;  and  when 


Of  Chimney  Fireplaces.  5 1 3 

this  is  done,  if  the  opening  of  the  fireplace  should  be  only 
two  or  three  inches  too  wide,  —  that  is  to  say,  only  two 
or  three  inches  wider  than  is  necessary  in  order  that  the 
covings  may  be  brought  into  their  proper  position  with 
respect  to  the  back,  —  I  should  not  alter  the  width  of  this 
opening,  but  should  accommodate  the  covings  to  this 
width,  by  increasing  their  breadth,  and  increasing  the 
angle  they  make  with  the  back  of  the  fireplace ;  but  if 
the  opening  of  the  fireplace  should  be  more  than  three 
inches  too  wide,  I  should  reduce  it  to  the  proper  width 
by  slips  of  stone,  or  by  bricks  and  mortar. 

When  the  width  of  the  opening  of  the  fireplace  in 
front  is  very  great  compared  with  the  depth  of  the  fire- 
place, and  with  the  width  of  the  back,  the  covings  in 
that  case  being  very  wide  and  consequently  very 
oblique,  and  the  fireplace  very  shallow,  any  sudden 
motion  of  the  air  in  front  of  the  fireplace  (that  motion, 
for  instance,  which  would  be  occasioned  by  the  clothes 
of  a  woman  passing  hastily  before  the  fire,  and  very 
near  it)  would  be  apt  to  cause  eddies  in  the  air,  within 
the  opening  of  the  fireplace,  by  which  puffs  of  smoke  might 
easily  be  brought  into  the  room. 

Should  the  opening  of  the  chimney  be  too  narrow, 
which  however  will  seldom  be  found  to  be  the  case,  it 
will,  in  general,  be  advisable  to  let  it  remain  as  it  is,  and 
to  accommodate  the  covings,  to  it,  rather  than  to  attempt 
to  increase  its  width,  which  would  be  attended  with  a 
good  deal  of  trouble,  and  probably  a  considerable 
expense. 

From  all  that  has  been  said,  it  is  evident  that  the 
points  of  the  greatest  importance,  and  which  ought 
most  particularly  to  be  attended  to  in  altering  fireplaces 
upon  the  principles  here  recommended,  are,  the  bringing 

VOL.  n.  33 


514  Of  Chimney  Fireplaces. 

forward  the  back  to  its  proper  place,  and  making  it  of  a 
proper  width.  But  it  is  time  that  I  should  mention 
another  matter  upon  which  it  is  probable  that  my  reader 
is  already  impatient  to  receive  information.  Provision 
must  be  made  for  the  passage  of  the  chimney-sweeper 
up  the  chimney.  This  may  easily  be  done  in  the  fol- 
lowing manner.  In  building  up  the  new  back  of  the 
fireplace,  —  when  this  wall  (which  need  never  be  more 
than  the  width  of  a  single  brick  in  thickness)  is 
brought  up  so  high  that  there  remains  no  more  than 
about  ten  or  eleven  inches  between  what  is  then  the  top 
of  it  and  the  inside  of  the  mantle,  or  lower  extremity 
of  the  breast  of  the  chimney,  —  an  opening,  or  door- 
way, eleven  or  twelve  inches  wide,  must  be  begun  in  the 
middle  of  the  back,  and  continued  quite  to  the  top  of 
it,  which,  according  to  the  height  to  which  it  will  com- 
monly be  necessary  to  carry  up  the  back,  will  make  the 
opening  about  twelve  or  fourteen  inches  high ;  which 
will  be  quite  sufficient  to  allow  the  chimney-sweeper  to 
pass.  When  the  fireplace  is  finished,  this  doorway  is  to 
be  closed  by  a  few  bricks,  by  a  tile,  or  a  fit  piece  of 
stone,  placed  in  it,  dry  or  without  mortar,  and  confined 
in  its  place  by  means  of  a  rabbet  made  for  that  purpose 
in  the  brick-work.  As  often  as  the  chimney  is  swept, 
the  chimney-sweeper  takes  down  this  temporary  wall, 
which  is  very  easily  done,  and  when  he  has  finished  his 
work  he  puts  it  again  into  its  place.  The  annexed 
drawing  (Plate  X.,  Fig.  6)  will  give  a  clear  idea  of  this 
contrivance ;  and  the  experience  I  have  had  of  it  has 
proved  that  it  answers  perfectly  well  the  purpose  for 
which  it  is  designed. 

I   observed  above,   that  the  new  back,  which  it  will 
always  be  found  necessary  to  build  in  order  to  bring  the 


Of  Chimney  Fireplaces.  5 1 5 

fire  sufficiently  forward,  in  altering  a  chimney  con- 
structed on  the  common  principles,  need  never  be 
thicker  than  the  width  of  a  common  brick.  I  may  say 
the  same  of  the  thickness  necessary  to  be  given  to  the 
new  sides,  or  covings,  of  the  chimney;  or  if  the  new 
back  and  covings  are  constructed  of  stone,  one  inch  and 
three  quarters,  or  two  inches,  in  thickness,  will  be  suffi- 
cient. Care  should  be  taken  in  building  up  these  new 
walls  to  unite  the  back  to  the  covings  in  a  solid  manner. 

Whether  the  new  back  and  covings  are  constructed 
of  stone,  or  built  of  bricks,  the  space  between  them 
and  the  old  back  and  covings  of  the  chimney  ought  to 
be  filled  up,  to  give  greater  solidity  to  the  structure. 
This  may  be  done  with  loose  rubbish,  or  pieces  of 
broken  bricks,  or  stones,  provided  the  work  be  strength- 
ened by  a  few  layers  or  courses  of  bricks  laid  in  mortar ; 
but  it  will  be  indispensably  necessary  to  finish  the  work, 
where  these  new  walls  end,  that  is  to  say,  at  the  top  of 
the  throat  of  the  chimney,  where  it  ends  abruptly  in  the 
open  canal  of  the  chimney,  by  a  horizontal  course  of 
bricks  well  secured  with  mortar.  This  course  of  bricks 
will  be  upon  a  level  with  the  top  of  the  doorway  left  for 
the  chimney-sweeper.  , 

From  these  descriptions  it  is  clear,  that,  where  the 
throat  of  the  chimney  has  an  end,  that  is  to  say,  where 
it  enters  into  the  lower  part  of  the  open  canal  of  the 
chimney,  there  the  three  walls  which  form  the  two  cov- 
ings and  the  back  of  the  fireplace  all  end  abruptly.  It 
is  of  much  importance  that  they  should  end  in  this 
manner  ;  for  were  they  to  be  sloped  outward  and  raised 
in  such  a  manner  as  to  swell  out  the  upper  extremity  of 
the  throat  of  the  chimney  in  the  form  of  a  trumpet,  and 
increase  it  by  degrees  to  the  size  of  the  canal  of  the 


5 1 6  Of  Chimney  Fireplaces. 

chimney,  this  manner  of  uniting  the  lower  extremity  of 
the  canal  of  the  chimney  with  the  throat  would  tend  to 
assist  the  winds  which  may  attempt  to  blow  down  the 
chimney,  in  forcing  their  way  through  the  throat,  and 
throwing  the  smoke  backward  into  the  room ;  but  when 
the  throat  of  the  chimney  ends  abruptly,  and  the  ends 
of  the  new  walls  form  a  flat  horizontal  surface,  it  will  be 
much  more  difficult  for  any  wind  from  above  to  find 
and  force  its  way  through  the  narrow  passage  of  the 
throat  of  the  chimney. 

As  the  two  walls  which  form  the  new  covings  of  the 
chimney  are  not  parallel  to  each  olher,  but  inclined, 
presenting  an  oblique  surface  towards  the  front  of  the 
chimney,  and  as  they  are  built  perfectly  upright  and 
quite  flat,  from  the  hearth  to  the  top  of  the  throat, 
where  they  end,  it  is  evident  that  a  horizontal  section 
of  the  throat  will  not  be  an  oblong  square ;  but  its 
deviation  from  that  form  is  a  matter  of  no  consequence ; 
and  no  attempts  should  ever  be  made,  by  twisting  the 
covings  above,  where  they  approach  the  breast  of  the 
chimney,  to  bring  it  to  that  form.  All  twists,  bends, 
prominences,  excavations,  and  other  irregularities  of 
form,  in  the  covings  of  a  chimney,  never  fail  to  pro- 
duce eddies  in  the  current  of  air  which  is  continually 
passing  into  and  through  an  open  fireplace  in  which  a 
fire  is  burning;  and  all  such  eddies  disturb  either  the 
fire,  or  the  ascending  current  of  smoke,  or  both,  and 
not  unfrequently  cause  the  smoke  to  be  thrown  back 
into  the  room.  Hence  it  appears,  that  the  covings  of 
chimneys  should  never  be  made  circular,  or  in  the  form 
of  any  other  curve,  but  always  quite  flat. 

For  the  same  reason,  that  is  to  say,  to  prevent  eddies, 
the  breast  of  the  chimney,  which  forms  that  side  of  the 


Of  Chimney  Fireplaces.  5 1 7 

throat  that  is  in  front,  or  nearest  to  the  room,  should 
he  neatly  cleaned  off,  and  its  surface  made  quite  regular 
and  smooth. 

This  may  easily  be  done  by  covering  it  with  a  coat 
of  plaster,  which  may  be  made  thicker  or  thinner  in 
different  parts  as  may  be  necessary  in  order  to  bring  the 
breast  of  the  chimney  to  be  of  the  proper  form. 

With  regard  to  the  form  of  the  breast  of  a  chimney, 
this  is  a  matter  of  very  great  importance,  and  which 
ought  always  to  be  particularly  attended  to.  The  worst 
form  it  can  have  is  that  of  a  vertical  plane,  or  upright 
flat ;  and  next  to  this,  the  worst  form  is  an  inclined 
plane.  Both  these  forms  cause  the  current  of  warm  air 
from  the  room,  which  will,  in  spite  of  every  precaution, 
sometimes  find  its  way  into  the  chimney,  to  cross  upon 
the  current  of  smoke,  which  rises  from  the  fire,  in  a 
manner  most  likely  to  embarrass  it  in  its  ascent,  and 
drive  it  back.  The  inclined  plane  which  is  formed  by  a 
flat  register  placed  in  the  throat  of  a  chimney  produces 
the  same  effects ;  and  this  is  one  reason,  among  many 
others,  which  have  induced  me  to  disapprove  of  register 
stoves. 

•  The  current  of  air,  which,  passing  under  the  mantle, 
gets  into  the  chimney,  should  be  made  gradually  to  bend 
its  course  upwards,  by  which  means  it  will  unite  quietly 
with  the  ascending  current  of  smoke,  and  will  be  less 
likely  to  check  it,  or  force  it  back  into  the  room.  Now 
this  may  be  effected  with  the  greatest  ease  and  certainty, 
merely  by  rounding  off  the  breast  of  the  chimney  or  back 
part  of  the  mantle,  instead  of  leaving  it  flat,  or  full  of 
holes  and  corners ;  and  this,  of  course,  ought  always  to 
be  done. 

I  have  hitherto  given  no  precise  directions  in  regard 


5 1 8  Of  Chimney  Fireplaces. 

to  the  height  to  which  the  new  back  and  covings  ought 
to  be  carried.  This  will  depend  not  only  on  the  height 
of  the  mantle,  but  also,  and  mpre  especially,  on  the 
height  of  the  breast  of  the  chimney,  or  of  that  part  of 
the  chimney  where  the  breast  ends  and  the  upright  canal 
begins.  The  back  and  covings  must  rise  a  few  inches,  5 
or  6  for  instance,  higher  than  this  part,  otherwise  the 
throat  of  the  chimney  will  not  be  properly  formed  ;  but  I 
know  of  no  advantages  that  would  be  gained  by  carry- 
ing them  up  still  higher. 

I  mentioned  above,  that  the  space  between  the  walls 
which  form  the  new  back  and  covings,  and  the  old  back 
and  sides  of  the  fireplace,  should  be  filled  up;  but  this 
must  not  be  understood  to  apply  to  the  space  between 
the  wall  of  dry  bricks,  or  the  tile  which  closes  the  passage 
for  the  chimney-sweeper,  and  the  old  back  of  the  chim- 
ney ;  for  that  space  must  be  left  void,  otherwise,  though 
this  tile  (which  at  most  will  not  be  more  than  two 
inches  in  thickness)  were  taken  away,  there  would  not 
be  room  sufficient  for  him  to  pass. 

In  forming  this  doorway,  the  best  method  of  proceed- 
ing is  to  place  the  tile  or  flat  piece  of  stone  destined  for 
closing  it  in  its  proper  place,  and  to  build  round  it,  or 
rather  by  the  sides  of  it,  taking  care  not  to  bring  any 
mortar  near  it,  in  order  that  it  may  be  easily  removed 
when  the  doorway  is  finished.  With  regard  to  the  rab- 
bet which  should  be  made  in  the  doorway  to  receive  it 
and  fix  it  more  firmly  in  its  place,  this  may  either  be 
formed  at  the  same  time  when  the  doorway  is  built,  or 
it  may  be  made  after  it  is  finished,  by  attaching  to  its 
bottom  and  sides,  with  strong  mortar,  pieces  of  thin 
roof  tiles.  Such  as  are  about  half  an  inch  in  thickness 
will  be  best  for  this  use ;  if  they  are  thicker,  they  will 


Of  Chimney  Fireplaces.  5 1 9 

diminish  too  much  the  opening  of  the  doorway,  and 
will  likewise  be  more  liable  to  be  torn  away  by  the 
chimney-sweeper  in  passing  up  and  down  the  chimney. 

It  will  hardly  be  necessary  for  me  to  add,  that  the 
tile,  or  flat  stone,  or  wall  of  dry  bricks,  which  is  used 
for  closing  up  this  doorway,  must  be  of  sufficient  height 
to  reach  quite  up  to  a  level  with  the  top  of  the  walls 
which  form  the  new  back  and  covings  of  the  chimneys. 

I  ought,  perhaps,  to  apologize  for  having  been  so 
very  particular  in  these  descriptions  and  explanations  ; 
but  it  must  be  remembered  that  this  chapter  is  written 
principally  for  the  information  of  those  who,  having 
had  few  opportunities  of  employing  their  attention  in 
abstruse  philosophical  researches,  are  not  sufficiently 
practised  in  these  intricate  investigations  to  seize,  with 
facility,  new  ideas,  and  consequently,  that  I  have  fre- 
quently been  obliged  to  labour  to  make  myself  under- 
stood. 

I  have  only  to  express  my  wishes  that  my  reader  may 
not  be  more  fatigued  with  this  labour  than  I  have  been  ; 
for  we  shall  then  most  certainly  be  satisfied  with  each 
other.  But  to  return  once  more  to  the  charge. 

There  is  one  important  circumstance  respecting  chim- 
ney fireplaces  destined  for  burning  coals,  which  still 
remains  to  be  further  examined ;  and  that  is  the  grate. 

Although  there  are  few  grates  that  may  not  be  used 
in  chimneys  constructed  or  altered  upon  the  principles 
here  recommended,  yet  they  are  not,  by  any  means,  all 
equally  well  adapted  for  that  purpose.  Those  whose 
construction  is  the  most  simple,  and  which,  of  course, 
are  the  cheapest,  are  beyond  comparison  the  best,  on  all 
accounts.  Nothing  being  wanted  in  these  chimneys  but 
merely  a  grate  for  containing  the  coals,  and  in  which 


520  Of  Chimney  Fireplaces. 

they  will  burn  with  a  clear  fire,  and  all  additional  appa- 
ratus being  not  only  useless,  but  very  pernicious,  all 
complicated  and  expensive  grates  should  be  laid  aside, 
and  such  as  are  more  simple  substituted  in  the  room  of 
them.  And  in  the  choice  of  a  grate,  as  in  everything 
else,  beauty  and  elegance  may  easily  be  united  with  the 
most  perfect  simplicity.  Indeed,  they  are  incompatible  with 
everything  else. 

In  placing  the  grate,  the  thing  principally  to  be 
attended  to  is  to  make  the  back  of  it  coincide  with  the 
back  of  the  fireplace  ;  but  as  many  of  the  grates  now  in 
common  use  will  be  found  to  be  too  large,  when  the 
fireplaces  are  altered  and  improved,  it  will  be  necessary 
to  diminish  their  capacities  by  filling  them  up  at  the 
back  and  sides  with  pieces  of  fire-stone.  When  this  is 
done,  it  is  the  front  of  the  flat  piece  of  fire-stone  which 
is  made  to  form  a  new  back  to  the  grate,  which  must  be 
made  to  coincide  with  and  mark  part  of  the  back 
of  the  fireplace.  But  in  diminishing  the  capacities  of 
grates  with  pieces  of  fire-stone,  care  must  be  taken  not 
to  make  them  too  narrow. 

The  proper  width  for  grates  destined  for  rooms  of  a 
middling  size  will  be  from  6  to  8  inches,  and  their 
length  may  be  diminished  more  or  less,  according  as  the 
room  is  heated  with  more  or  less  difficulty,  or  as  the 
weather  is  more  or  less  severe.  But  where  the  width  of 
a  grate  is  not  more  than  5  inches,  it  will  be  very  diffi- 
cult to  prevent  the  fire  from  going  out. 

It  goes  out  for  the  same  reason  that  a  live  coal  from 
the  grate  that  falls  upon  the  hearth  soon  ceases  to  be  red- 
hot  ;  it  is  cooled  by  the  surrounding  cold  air  of  the  at- 
mosphere. The  knowledge  of  the  cause  which  produces 
this  effect  is  important,  as  it  indicates  the  means  which 


Of  Chimney  Fireplaces.  521 

may  be  used  for  preventing  it.  But  of  this  subject  I 
shall  treat  more  fully  hereafter. 

It  frequently  happens  that  the  iron  backs  of  grates 
are  not  vertical,  or  upright,  but  inclined  backwards. 
When  these  grates  are  so  much  too  wide  as  to  render  it 
necessary  to  fill  them  up  behind  with  fire-stone,  the  in- 
clination of  the  back  will  be  of  little  consequence  ;  for 
by  making  the  piece  of  stone  with  which  the  width  of 
the  grate  is  to  be  diminished  in  the  form  of  a  wedge,  or 
thicker  above  than  below,  the  front  of  this  stone,  which 
in  effect  will  become  the  back  of  the  grate,  may  be 
made  perfectly  vertical,  and,  the  iron  back  of  the  grate 
being  hid  in  the  solid  work  of  the  back  of  the  fireplace, 
will  produce  no  effect  whatever;  but,  if  the  grate  be 
already  so  narrow  as  not  to  admit  of  any  diminution  of 
its  width,  in  that  case  it  will  be  best  to  take  away  the 
iron  back  of  the  grate  entirely,  and,  fixing  the  grate 
firmly  in  the  brickwork,  cause  the  back  of  the  fireplace 
to  serve  as  a  back  to  the  grate.  This  I  have  very  fre- 
quently done,  and  have  always  found  it  to  answer  per- 
fectly well. 

Where  it  is  necessary  that  the  fire  in  a  grate  should 
be  very  small,  it  will  be  best,  in  reducing  the  grate  with 
fire-stone,  to  bring  its  cavity,  destined  for  containing  the 
fuel,  to  the  form  of  one  half  of  a  hollow  hemisphere ; 
the  two  semicircular  openings  being  one  above,  to 
receive  the  coals,  and  the  other  in  front,  or  towards  the 
bars  of  the  grate ;  for  when  the  coals  are  burned  in  such 
a  confined  space,  and  surrounded  on  all  sides,  except  in 
the  front  and  above,  by  fire-stone  (a  substance  peculiarly 
well  adapted  for  confining  heat),  the  heat  of  the  fire  will 
be  concentrated,  and,  the  cold  air  of  the  atmosphere 
being  kept  at  a  distance,  a  much  smaller  quantity  of 


522  Of  Chimney  Fireplaces. 

coals  will  burn  than  could  possibly  be  made  to  burn  in 
a  grate  where  they  would  be  more  exposed  to  be  cooled 
by  the  surrounding  air,  or  to  have  their  heat  carried  off 
by  being  in  contact  with  iron,  or  with  any  other  sub- 
stance through  which  heat  passes  with  greater  facility 
than  through  fire-stone. 

Being  persuaded  that,  if  the  improvements  in  chimney 
fireplaces  here  recommended  should  be  generally  adopted 
(which  I  cannot  help  flattering  myself  will  be  the  case), 
it  will  become  necessary  to  reduce,  very  considerably, 
the  sizes  of  grates,  I  was  desirous  of  showing  how  this 
may,  with  the  greatest  safety  and  facility,  be  done. 

Where  grates,  which  are  designed  for  rooms  of  a 
middling  size,  are  longer  than  14  or  15  inches,  it  will 
always  be  best,  not  merely  to  diminish  their  lengths,  by 
filling  them  up  at  their  two  ends  with  fire-stone,  but, 
forming  the  back  of  the  chimney  of  a  proper  width, 
without  paying  any  regard  to  the  length  of  the  grate,  to 
carry  the  covings  through  the  two  ends  of  the  grate  in 
such  a  manner  as  to  conceal  them,  or  at  least  to  conceal 
the  back  corners  of  them  in  the  walls  of  the  covings. 

I  cannot  help  flattering  myself  that  the  directions 
here  given  in  regard  to  the  alterations  which  it  may  be 
necessary  to  make  in  fireplaces,  in  order  to  introduce 
the  improvements  proposed,  will  be  found  to  be  so 
perfectly  plain  and  intelligible  that  no  one  who  reads 
them  will  be  at  any  loss  respecting  the  manner  in  which 
the  work  is  to  be  performed ;  but  as  order  and  arrange- 
ment tend  much  to  facilitate  all  mechanical  operations, 
I  shall  here  give  a  few  short  directions  respecting  the 
manner  of  laying  out  the  work,  which  may  be  found  use- 
ful, and  particularly  to  gentlemen  who  may  undertake 
to  be  their  own  architects,  in  ordering  and  directing  the 


Of  Chimney  Fireplaces.  523 

alterations   to  be  made  for  the  improvement  of  their 
fireplaces. 

Directions  for  laying  out  the  Work. 

If  there  be  a  grate  in  the  chimney  which  is  to  be 
altered,  it  will  always  be  best  to  take  it  away ;  and  when 
this  is  done,  the  rubbish  must  be  removed,  and  the 
hearth  swept  perfectly  clean.  \ 

Suppose  the  annexed  figure  (Plate  VIII.,  Fig.  i)  to 
represent  the  ground  plan  of  such  a  fireplace;  A  B 
being  the  opening  of  it  in  front,  A  C  and  B  D  the  two 
sides  or  covings,  and  C  D  the  back. 

Figure  2  shows  the  elevation  of  this  fireplace. 

First,  draw  a  straight  line,  with  chalk  or  with  a  lead- 
pencil,  upon  the  hearth,  from  one  jamb  to  the  other, 
even  with  the  front  of  the  jambs.  The  dotted  line  A 
B  (Plate  IX.,  Fig.  3)  may  represent  this  line. 

From  the  middle  C  of  this  line  (A  B)  another  line 
c  d  is  to  be  drawn  perpendicular  to  it,  across  the  hearth, 
to  the  middle  d  of  the  back  of  the  chimney. 

A  person  must  now  stand  upright  in  the  chimney, 
with  his  back  to  the  back  of  the  chimney,  and  hold  a 
plumb-line  to  the  middle  of  the  upper  part  of  the  breast 
of  the  chimney  (Plate  X.,  Fig.  5,  d\  or  where  the  canal 
of  the  chimney  begins  to  rise  perpendicularly ;  taking 
care  to  place  the  line  above  in  such  a  manner  that  the 
plumb  may  fall  on  the  line  c  d^  drawn  on  the  hearth  from 
the  middle  of  the  opening  of  the  chimney  in  front  to 
the  middle  of  the  back,  and  an  assistant  must  mark  the 
precise  place  e>  on  that  line  where  the  plumb  falls. 

This  being  done,  and  the  person  in  the  chimney  hav- 
ing quitted  his  station,  4  inches  are  to  be  set  off  on 
the  line  c  d,  from  e  towards  d;  and  the  point  /,  where 


524  Of  Chimney  Fireplaces. 

these  4  inches  end  (which  must  be  marked  with  chalk, 
or  with  a  pencil),  will  show  how  far  the  new  back  is  to 
be  brought  forward. 

Through /"draw  the  lineg  hy  parallel  to  the  line  A  B, 
and  this  line  g  h  will  show  the  direction  of  the  new 
back,  or  the  ground  line  upon  which  it  is  to  be  built. 

The  line  cf  will  show  the  depth  of  the  new  fireplace ; 
and  if  it  should  happen  that  f /is  equal  to  about  one 
third  of  the  line  A  B,  and  if  the  grate  can  be  accom- 
modated to  the  fireplace  instead  of  its  being  necessary 
to  accommodate  the  fireplace  to  the  grate,  in  that  case 
half  the  length  of  the  line  cfis  to  be  set  off  from  /on 
the  line  g  f  h>  on  one  side  to  k,  and  on  the  other  to  /, 
and  the  line  /  k  will  show  the  ground  line  of  the  fore- 
part of  the  back  of  the  chimney. 

In  all  cases  where  the  width  of  the  opening  of  the 
fireplace  in  front  (A  B)  happens  to  be  not  greater,  or 
not  more  than  two  or  three  inches  greater,  than  three 
times  the  width  of  the  new  back  of  the  chimney  (/'  k\ 
this  opening  may  be  left,  and  lines  drawn  from  /  to 
A  and  from  k  to  B  will  show  the  width  and  position 
of  the  front  of  the  new  covings  ;  but  when  the  open- 
ing of  the  fireplace  in  front  is  still  wider,  it  must  be 
reduced,  which  is  to  be  done  in  the  following  manner. 

From  c,  the  middle  of  the  line  A  B,  c  a  and  c  b 
must  be  set  off  equal  to  the  width  of  the  back  (/  k\ 
added  to  half  its  width  (//),  and  lines  drawn  from  /  to 
a  and  from  k  to  b  will  show  the  ground  plan  of 
the  fronts  of  the  new  covings. 

When  this  is  done,  nothing  more  will  be  necessary 
than  to  build  up  the  back  and  covings,  and,  if  the  fire- 
place is  designed  for  burning  coals,  to  fix  the  grate  in  its 
proper  place,  according  to  the  directions  already  given. 


Of  Chimn  y  Fireplaces.  525 

When  the  width  of  the  fireplace  is  reduced,  the  edges 
of  the  covings  a  A  and  b  B  are  to  make  a  finish  with 
the  front  of  the  jambs.  And  in  general  it  will  be  best, 
not  only  for  the  sake  of  the  appearance  of  the  chimney, 
but  for  other  reasons  also,  to  lower  the  height  of  the 
opening  of  the  fireplace,  whenever  its  width  in  front  is 
diminished. 

Fig.  4  (Plate  IX.)  shows  a  front  view  of  the  chimney 
after  it  has  been  altered  according  to  the  directions  here 
given.  By  comparing  it  with  Fig.  i  (which  shows  a 
front  view  of  the  same  chimney  before  it  was  altered), 
the  manner  in  which  the  opening  of  the  fireplace  in 
front  is  diminished  may  be  seen.  In  Fig.  4,  the  under 
part  of  the  doorway  by  which  the  chimney-sweeper  gets 
up  the  chimney  is  represented  by  white  dotted  lines. 
The  doorway  is  represented  closed. 

I  shall  finish  this  chapter  with  some  general  observa- 
tions relative  to  the  subject  under  consideration  ;  with 
directions  how  to  proceed  where  such  local  circum- 
stances exist  as  render  modifications  of  the  general  plan 
indispensably  necessary. 

Whether  a  chimney  be  designed  for  burning  wood 
upon  the  hearth,  or  wood  or  coals  in  a  grate,  the  form 
of  the  fireplace  is,  in  my  opinion,  most  perfect  when 
the  width  of  the  back  is  equal  to  the  depth  of  the  fireplace, 
and  the  opening  of  the  fireplace  in  front  equal  to  three 
times  the  width  of  the  back,  or,  which  is  the  same  thing, 
to  three  times  the  depth  of  the  fireplace. 

But  if  the  chimney  be  designed  for  burning  wood 
upon  the  hearth,  upon  handirons,  or  dogs,  as  they  are 
called,  it  will  sometimes.be  necessary  to  accommodate 
the  width  of  the  back  to  the  length  of  the  wood ;  and 
when  this  is  the  case,  the  covings  must  be  accommodated 


526  Of  Chimney  Fireplaces. 

to  the  width  of  the  back  and  the  opening  of  the  chim- 
ney in  front. 

When  the  wall  of  the  chimney  in  front,  measured 
from  the  upper  part  of  the  breast  of  the  chimney  to  the 
front  of  the  mantle,  is  very  thin,  it  may  happen,  and 
especially  in  chimneys  designed  for  burning  wood  upon 
the  hearth,  or  upon  dogs,  that  the  depth  of  the  chim- 
ney, determining  according  to  the  directions  here  given, 
may  be  too  small. 

Thus,  for  example,  supposing  the  wall  of  the  chimney 
in  front,  from  the  upper  part  of  the  breast  of  the  chim- 
ney to  the  front  of  the  mantle,  to  be  only  4  inches 
(which  is  sometimes  the  case,  particularly  in  rooms  situ- 
ated near  the  top  of  a  house),  in  this  case,  if  we  take 
4  inches  for  the  width  of  the  throat,  this  will  give  8 
inches  only  for  the  depth  of  the  fireplace,  which  would 
be  too  little,  even  were  coals  to  be  burned  instead  of 
wood.  In  this  case  I  should  increase  the  depth  of  the 
fireplace  at  the  hearth  to  12  or  13  inches,  and  should 
build  the  back  perpendicular  to  the  height  of  the  top  of 
the  burning  fuel  (whether  it  be  wood  burned  upon  the 
hearth,  or  coals  in  a  grate),  and  then,  sloping  the  back 
by  a  gentle  inclination  forward,  bring  it  to  its  proper 
place,  that  is  to  say,  •perpendicularly  under  the  back  part  of 
the  throat  of  the  chimney.  This  slope  (which  will  bring 
the  back  forward  4  or  5  inches,  or  just  as  much  as  the 
depth  of  the  fireplace  is  increased),  though  it  ought  not 
to  be  too  abrupt,  yet  it  ought  to  be  quite  finished  at  the 
height  of  8  or  10  inches  above  the  fire,  otherwise  it  may 
perhaps  cause  the  chimney  to  smoke ;  but  when  it  is 
very  near  the  fire,  the  heat  of  the  fire  will  enable  the 
current  of  rising  smoke  to  overcome  the  obstacle  which 
this  slope  will  oppose  to  its  ascent,  which  it  could  not 


Of  Chimney  Fireplaces.  527 

do  so  easily  were  the  slope  situated  at  a  greater  distance 
from  the  burning  fuel.* 

Figs.  7,  8,  and  9  (Plate  X.)  show  a  plan,  elevation, 


*  Having  been  obliged  to  carry  backward  the  fireplace  in  the  manner  here 
described,  in  order  to  accommodate  it  to  a  chimney  whose  walls  in  front  were 
remarkably  thin,  I  was  surprised  to  find,  upon  lighting  the  fire,  that  it  appeared  to 
give  out  more  heat  into  the  room  than  any  fireplace  I  had  ever  constructed.  This 
effect  was  quite  unexpected ;  but  the  cause  of  it  was  too  obvious  not  to  be  immedi- 
ately discovered.  The  flame  rising  from  the  fire  broke  against  the  part  of  the  back 
which  sloped  forward  over  the  fire,  and  this  part  of  the  back  being  soon  very  much 
heated,  and  in  consequence  of  its  being  very  hot,  (and  when  the  fire  burned  bright  it 
was  frequently  quite  red-hot,)  it  threw  off  into  the  room  a  great  deal  of  radiant  heat. 
It  is  not  possible  that  this  oblique  surface  (the  slope  of  the  back  of  the  fireplace) 
could  have  been  heated  red-hot  merely  by  the  radiant  heat  projected  by  the  burning 
fuel ;  for  other  parts  of  the  fireplace  nearer  the  fire,  and  better  situated  for  receiving 
radiant  heat,  were  never  found  to  be  so  much  heated  j  and  hence  it  appears  that  the 
combined  heat  in  the  current  of  smoke  and  hot  vapour  which  rises  from  an  open  fire 
may  be,  at  least  in  fart,  stopped  in  its  passage  up  the  chimney,  changed  into  radiant 
heat,  and  afterwards  thrown  into  the  room.  This  opens  a  new  and  very  interesting 
field  for  experiment,  and  bids  fair  to  lead  to  important  improvements  in  the  construc- 
tion of  fireplaces.  I  have  of  late  been  much  engaged  in  these  investigations,  and  am 
now  actually  employed  daily  in  making  a  variety  of  experiments  with  grates  and  fire- 
places, upon  different  constructions,  in  the  room  I  inhabit  in  the  Royal  Hotel  in  Pall 
Mall ;  and  Mr.  Hopkins,  of  Greek  Street,  Soho,  Ironmonger  to  his  Majesty,  and 
Mrs.  Hempel,  at  her  Pottery  at  Chelsea,  are  both  at  work  in  their  different  lines  of 
business,  under  my  direction,  in  the  construction  of  fireplaces  upon  a  principle  entirely 
new,  and  which,  I  flatter  myself,  will  be  found  to  be  not  only  elegant  and  convenient, 
but  very  economical.  But  as  I  mean  soon  to  publish  a  particular  account  of  these 
fireplaces,  with  drawings  and  ample  directions  for  constructing  them,  I  shall  not 
enlarge  further  on  the  subject  in  this  place.'  It  may,  however,  not  be  amiss  just  to 
mention  here,  that  these  new  invented  fireplaces  not  being  fixed  to  the  walls  of  the 
chimney,  but  merely  set  down  upon  the  hearth,  may  be  used  in  any  open  chimney ; 
and  that  chimneys  altered  or  constructed  on  the  principles  here  recommended  are  par- 
ticularly well  adapted  for  receiving  them. 

The  public  in  general,  and  more  particularly  those  tradesmen  and  manufacturers 
whom  it  may  concern,  are  requested  to  observe,  that,  as  the  author  does  not  intend  to 
take  out  himself,  or  to  surfer  others  to  take  out,  any  patent  for  any  invention  of  his 
which  may  be  of  public  utility,  all  persons  are  at  full  liberty  to  imitate  them,  and 
vend  them,  for  their  own  emolument,  when  and  where  and  in  any  way  they  may 
think  proper;  and  those  who  may  wish  for  any  further  information  rejpccting  any  of 
those  inventions  or  improvements  will  receive  (gratis)  all  the  information  they  can 
require  by  applying  to  the  author,  who  will  take  pleasure  in  giving  them  every  assist- 
ance in  his  power. 


528  Of  Chimney  Fireplaces. 

and  section  of  a  fireplace  constructed  or  altered  upon 
this  principle.  The  wall  of  the  chimney  in  front  at  a 
(Fig.  9)  being  only  4  inches  thick,  4  inches  more  added 
to  it  for  the  width  of  the  throat  would  have  left  the 
depth  of  the  fireplace  measured  upon  the  hearth  b  c  only 
8  inches,  which  would  have  been  too  little;  a  niche  c 
and  e  was  therefore  made  in  the  new  back  of  the  fire- 
place for  receiving  the  grate,  which  niche  was  6  inches 
deep  in  the  centre  of  it,  below  13  inches  wide  (or  equal 
in  width  to  the  grate),  and  23  inches  high ;  finishing 
above  with  a  semicircular  arch,  which,  in  its  highest 
part,  rose  7  inches  above  the  upper  part  of  the  grate. 
The  doorway  for  the  chimney-sweeper,  which  begins 
just  above  the  top  of  the  niche,  may  be  seen  distinctly 
in  both  the  Figs.  8  and  9.  The  space  marked  £  (Fig. 
9)  behind  this  doorway  may  either  be  filled  with  loose 
bricks,  or  may  be  left  void.  The  manner  in  which  the 
piece  of  stone  (f,  Fig.  9)  which  is  put  under  the  mantle 
of  the  chimney  to  reduce  the  height  of  the  opening  of 
the  fireplace,  is  rounded  off  on  the  inside,  in  order  to 
give  a  fair  run  to  the  column  of  smoke  in  its  ascent 
through  the  throat  of  the  chimney,  is  clearly  expressed 
in  this  figure. 

The  plan  (Fig.  7)  and  elevation  (Fig.  8)  show  how 
much  the  width  of  the  opening  of  the  fireplace  in  front 
is  diminished,  and  how  the  covings  in  the  new  fireplace 
are  formed. 

A  perfect  idea  of  the  form  and  dimension  of  the  fire- 
place in  its  original  state,  as  also  after  its  alteration,  may 
be  had  by  a  careful  inspection  of  these  figures. 

I  have  added  the  drawing  (Fig.  10,  Plate  XI.)  merely 
to  show  how  a  fault,  which  I  have  found  workmen  in 
general  whom  I  have  employed  in  altering  fireplaces  are 


Of  Ch  im  ney  Fireplaces.  529 

very  apt  to  commit,  is  to  be  avoided.  In  chimneys  like 
that  represented  in  this  figure,  where  the  jambs  A  and  B 
project  far  into  the  room,  and  where  the  front  edge  of 
the  marble  slab  <?,  which  forms  the  coving,  does  not 
come  so  far  forward  as  the  front  of  the  jambs,  the  work- 
men in  constructing  the  new  covings  are  very  apt  to 
place  them,  not  in  the  line  c  A,  which  they  ought  to  do, 
but  in  the  line  c  o,  which  is  a  great  fault.  The  covings 
of  a  chimney  should  never  range  behind  the  front  of  the 
jambs,  however  those  jambs  may  project  into  the  room; 
but  it  is  not  absolutely  necessary  that  the  covings  should 
make  a  finish  with  the  internal  front  corners  of  the 
jambs,  or  that  they  should  be  continued  from  the  back 
c  quite  to  the  front  of  the  jambs  at  A.  They  may 
finish  in  front  at  a  and  by  and  small  corners,  A,  0,  a,  may 
be  left  for  placing  the  shovels,  tongs,  etc. 

Were  the  new  coving  to  range  with  the  front  edge  of 
the  old  coving  <?,  the  obliquity  of  the  new  coving  would 
commonly  be  too  great ;  or  the  angle  d  c  o  would  exceed 
135  degrees,  which  it  never  should  do y  or  at  least  never  by 
more  than  a  very  few  degrees. 

No  inconvenience  of  any  importance  will  arise  from 
making  the  obliquity  of  the  covings  less  than  what  is 
here  recommended;  but  many  cannot  fail  to  be  pro- 
duced by  making  it  much  greater ;  and  as  I  know  from 
experience  that  workmen  are  very  apt  to  do  this,  I  have 
thought  it  necessary  to  warn  them  particularly  against  it. 

Fig.  1 1  shows  how  the  width  and  obliquity  of  the 
covings  of  a  chimney  are  to  be  accommodated  to  the 
width  of  the  back,  and  to  the  opening  in  front  and 
depth  of  the  fireplace,  where  the  width  of  the  opening 
of  the  fireplace  is  less  than  three  times  the  width  of  the 
new  back. 

VOL.  ii.  34 


53°  Of  Chimney  Fireplaces. 

As  all  those  who  may  be  employed  in  altering  chim- 
neys may  not  perhaps  know  how  to  set  off  an  angle  of  any 
certain  number  of  degrees,  or  may  not  have  at  hand  the 
instruments  necessary  for  doing  it,  I  shall  here  show 
how  an  instrument  may  be  made  which  will  be  found  to 
be  very  useful  in  laying  out  the  work  for  the  brick- 
layers. 

Upon  a  board  about  18  inches  wide  and  4  feet  long, 
or  upon  the  floor  or  a  table,  draw  three  equal  squares 
(A,  B,  C,  Fig.  12,  Plate  XIII.),  of  about  12  or  14 
inches  each  side,  placed  in  a  straight  line,  and  touching 
each  other.  From  the  back  corner  c  of  the  centre 
square  B  draw  a  diagonal  line  across  the  square  A,  to  its 
outward  front  corner  f,  and  the  adjoining  angle  formed 
by  the  lines  d  c  and  c/will  be  equal  to  135  degrees,  the 
angle  which  the  plane  of  the  back  of  a  chimney  fire- 
place ought  to  make  with  the  plane  of  its  covings.  And 
a  bevel  m  n  being  made  to  this  angle  with  thin  slips  of 
hard  wood,  this  little  instrument  will  be  found  to  be 
very  useful  in  marking  out  on  the  hearth,  with  chalk, 
the  plans  of  the  walls  which  are  to  form  the  covings  of 
fireplaces. 

As  chimneys  which  are  apt  to  smoke  will  require  the 
covings  to  be  placed  less  obliquely  in  respect  to  the 
back  than  others  which  have  not  that  defect,  it  would  be 
convenient  to  be  provided  with  several  bevels,  —  three 
or  four,  for  instance,  forming  different  angles.  That 
already  described,  which  may  be  called  No.  i,  will 
measure  the  obliquity  of  the  covings  when  the  fireplace 
can  be  made  of  the  most  perfect  form  ;  another,  No.  2, 
may  be  made  to  a  smaller  angle,  dee;  and  another,  No. 
3,  for  chimneys  which  are  very  apt  to  smoke,  at  the  still 
smaller  angle  d  c  i.  Or  a  bevel  may  be  so  contrived,  by 


Of  C/i  im  ney  Fireplaces.  531 

means  of  a  joint,  and  an  arch,  properly  graduated,  as  to 
serve  for  all  the  different  degrees  of  obliquity  which  it 
may  ever  be  necessary  to  give  to  the  covings  of  fire- 
places. 

Another  point  of  much  importance,  and  particularly 
•  in  chimneys  which  are  apt  to  smoke,  is  to  form  the 
throat  of  the  chimney  properly,  by  carrying  up  the 
back  and  covings  to  a  proper  height. 

This  workmen  are  apt  to  neglect  to  do,  probably  on 
account  of  the  difficulty  they  find  in  working  where  the 
opening  of  the  canal  of  the  chimney  is  so  much  re- 
duced. But  it  is  absolutely  necessary  that  these  walls 
should  be  carried  up  5  or  6  inches  at  least  above  the 
upper  part  of  the  breast  of  the  chimney,  or  to  that 
point  where  the  wall  which  forms  the  front  of  the  throat 
begins  to  rise  perpendicularly.  If  the  workman  has  in- 
telligence enough  to  avail  himself  of  the  opening  which 
is  formed  in  the  back  of  the  fireplace  to  give  a  passage 
to  the  chimney-sweeper,  he  will  find  little  difficulty  in 
finishing  his  work  in  a  proper  manner. 

In  placing  the  plumb-line  against  the  breast  of  the 
chimney,  in  order  to  ascertain  how  far  the  new  back  is 
to  be  brought  forward,  great  care  must  be  taken  to 
place  it  at  the  very  top  of  the  breast,  where  the  canal 
of  the  chimney  begins  to  rise  perpendicularly ;  otherwise, 
when  the  plumb-line  is  placed  too  low,  or  against  the 
slope  of  the  breast,  when  the  new  back  comes  to  be 
raised  to  its  proper  height,  the  throat  of  the  chimney 
will  be  found  to  be  too  narrow. 

Sometimes,  and  indeed  very  often,  the  top  of  the 
breast  of  a  chimney  lies  very  high,  or  far  above  the  fire 
(see  Figs.  13  and  14,  Plate  XIII.,  where  d  shows  the 
top  of  the  breast  of  the  chimney) ;  when  this  is  the  case, 


532  Of  Chimney  Fireplaces. 

it  must  be  brought  lower,  otherwise  the  chimney  will  be 
very  apt  to  smoke.  So  much  has  been  said,  in  the  first 
chapter  of  this  essay,  of  the  advantages  to  be  derived 
from  bringing  the  throat  of  a  chimney  near  to  the  burn- 
ing fuel,  that  I  do  not  think  it  necessary  to  enlarge 
on  them  in  this  place,  taking  it  for  granted  that  the 
utility  and  necessity  of  that  arrangement  have  already 
been  made  sufficiently  evident;  but  a  few  directions  for 
workmen,  to  show  them  how  the  breast  (and  conse- 
quently the  throat)  of  a  chimney  can  most  readily  be 
lowered,  may  not  be  superfluous. 

Where  the  too  great  height  of  the  breast  of  a  chimney 
is  owing  to  the  great  height  of  the  mantle  (see  Fig.  13), 
or,  which  is  the  same  thing,  of  the  opening  of  the  fire- 
place in  front,  which  will  commonly  be  found  to  be  the 
case,  the  only  remedy  for  the  evil  will  be  to  bring  down 
the  mantle  lower;  or,  rather,  to  make  the  opening  of 
the  fireplace  in  front  lower,  by  throwing  across  the  top 
of  this  opening,  from  one  jamb  to  the  other,  and  im- 
mediately under  the  mantle,  a  very  flat  arch,  a  wall  of 
bricks  and  mortar,  supported  on  straight  bars  of  iron, 
or  a  piece  of  stone  (/^,  Fig.  13).  When  this  is  done, 
the  slope  of  the  old  throat  of  the  chimney,  or  of  the 
back  side  of  the  mantle,  is  to  be  filled  up  with  plaster, 
so  as  to  form  one  continued  flat,  vertical,  or  upright 
plane  surface  with  the  lower  part  of  the  wall  of  the  canal 
of  the  chimney,  and  a  new  breast  is  to  be  formed  lower 
down,  care  being  taken  to  round  it  off  properly,  and 
make  it  finish  at  the  lower  surface  of  the  new  wall  built 
under  the  mantle;  which  wall  forms,  in  fact,  a  new  mantle. 

The  annexed  drawing  (Fig.  13),  which  represents  the 
section  of  a  chimney  in  which  the  breast  has  been 
lowered  according  to  the  method  here  described,  will 


Of  Chimney  Fireplaces.  533 

show  these  various  alterations  in  a  clear  and  satisfactory 
manner.  In  this  figure,  as  well  as  in  most  of  the  others 
in  this  essay,  the  old  walls  are  distinguished  from  the 
new  ones  by  the  manner  in  which  they  are  shaded;  the 
old  walls  being  shaded  by  diagonal  lines,  and  the  new 
ones  by  vertical  lines.  The  additions,  which  are  formed 
of  plaster,  are  shaded  by  dots  instead  of  lines. 

Where  the  too  great  height  of  the  breast  of  a  chimney 
is  occasioned,  not  by  the  height  of  the  mantle,  but  by 
the  too  great  width  of  the  breast,  in  that  case  (which, 
however,  will  seldom  be  found  to  occur),  this  defect 
may  be  remedied  by  covering  the  lower  part  of  the 
breast  with  a  thick  coating  of  plaster,  supported,  if 
necessary,  by  nails  or  studs  driven  into  the  wall  which 
forms  the  breast,  and  properly  rounded  off  at  the  lower 
part  of  the  mantle.  (See  Fig.  14.) 


CHAPTER    III. 

Of  the  Cause  of  the  Ascent  of  Smoke.  —  Illustration  of  the 
Subject  by  familiar  Comparisons  and  Experiments.  —  Of 
Chimneys  which  affect  and  cause  each  other  to  smoke.  —  Of 
Chimneys  which  smoke  from  Want  of  Air.  —  Of  the  Eddies 
of  Wind  which  sometimes  blow  down  Chimneys^  and  cause 
them  to  smoke. 


T 


HOUGH  it  was  my  wish  to  avoid  all  abstruse 
_  philosophical  investigations  in  this  essay,  yet  I 
feel  that  it  is  necessary  to  say  a  few  words  upon  a  sub- 
ject generally  considered  as  difficult  to  be  explained, 
which  is  too  intimately  connected  with  the  matter  under 


534  Of  Chimney  Fireplaces. 

consideration  to  be  passed  over  in  silence.  A  knowl- 
edge of  the  cause  of  the  ascent  of  smoke  being  indis- 
pensably necessary  to  those  who  engage  in  the  improve- 
ment of  fireplaces,  or  who  are  desirous  of  forming  just 
ideas  relative  to  the  operations  of  fire  and  the  manage- 
ment of  heat,  I  shall  devote  a  few  pages  to  the  investi- 
gation of  that  curious  and  interesting  subject.  And  as 
many  of  those  who  may  derive  advantage  from  these  in- 
quiries are  not  much  accustomed  to  philosophical  dis- 
quisitions, and  would  not  readily  comprehend  either  the 
language  or  the  diagrams  commonly  used  by  scientific 
writers  to  explain  the  phenomena  in  question,  I  shall 
take  pains  to  express  myself  in  the  most  familiar  man- 
ner, and  to  use  such  comparisons  for  illustration  as  may 
easily  be  understood. 

If  small  leaden  bullets,  or  large  goose-shot,  be  mixed 
with  peas,  and  the  whole  well  shaken  in  a  bushel,  the 
shot  will  separate  from  the  peas,  and  will  take  its  place 
at  the  bottom  of  the  bushel ;  forcing,  by  its  greater 
weight,  the  peas,  which  are  lighter,  to  move  upwards,  con- 
trary to  their  natural  tendency,  and  take  their  places  above. 

If  water  and  linseed  oil,  which  is  lighter  than  water, 
be  mixed  in  a  vessel  by  shaking  them  together,  upon 
suffering  this  mixture  to  remain  quiet  the  water  will 
descend  and  occupy  the  bottom  of  the  vessel,  and  the 
oil,  being  forced  out  of  its  place  by  the  greater  pressure 
downwards  of  the  heavier  liquid,  will  be  obliged  to  rise 
and  swim  on  the  surface  of  the  water. 

If  a  bottle  containing  linseed  oil  be  plunged  in  water 
with  its  mouth  upwards,  and  open,  the  oil  will  ascend 
out  of  the  bottle,  and,  passing  upwards  through  the  mass 
of  water,  in  a  continued  stream,  will  spread  itself  over 
its  surface. 


Of  Chimney  Fireplaces.  535 

In  like  manner,  when  two  fluids  of  any  kind,  of  dif- 
ferent densities,  come  into  contact,  or  are  mixed  with 
each  other,  that  which  is  the  lightest  will  be  forced  up- 
wards by  that  which  is  the  heaviest. 

And  as  heat  rarefies  all  bodies,  fluids  as  well  as  solids, 
air  as  well  as  water  or  mercury,  it  follows  that  two  por- 
tions of  the  same  fluid,  at  different  temperatures,  being 
brought  into  contact  with  each  other,  that  portion  which 
is  the  hottest,  being  more  rarified,  or  specifically  lighter 
than  that  which  is  colder,  must  be  forced  upwards  by  this 
last.  And  this  is  what  always  happens  in  fact. 

When  hot  water  and  cold  water  are  mixed,  the  hottest 
part  of  the  mixture  will  be  found  to  be  at  the  surface 
above ;  and  when  cold  air  is  admitted  into  a  warmed 
room,  it  will  always  be  found  to  take  its  place  at  the 
bottom  of  the  room,  the  warmer  air  being  in  part  ex- 
pelled, and  in  part  forced  upwards  to  the  top  of  the 
room. 

Both  air  and  water  being  transparent  and  colourless 
fluids,  their  internal  motions  are  not  easily  discovered 
by  the  sight ;  and  when  these  motions  are  very  slow, 
they  make  no  impression  whatever  on  any  of  our  senses, 
consequently  they  cannot  be  detected  by  us  without  the 
aid  of  some  mechanical  contrivance.  But  where  we 
have  reason  to  think  that  those  motions  exist,  means 
should  be  sought,  and  may  often  be  found,  for  render- 
ing them  perceptible. 

If  a  bottle  containing  hot  water  tinged  with  logwood, 
or  any  other  colouring  drug,  be  immersed,  with  its 
mouth  open,  and  upwards,  into  a  deep  glass  jar  filled 
with  cold  water,  the  ascent  of  the  hot  water  from  the 
bottle  through  the  mass  of  cold  water  will  be  perfectly 
visible  through  the  glass.  Now,  nothing  can  be  more 


536  Of  Chimney  Fireplaces. 

evident  than  that  both  of  these  fluids  are  forced  or 
pushed,,  and  not  drawn  upwards.  Smoke  is  frequently 
said  to  be  drawn  up  the  chimney,  and  that  a  chimney 
draws  well  or  ill;  but  these  are  careless  expressions, 
and  lead  to  very  erroneous  ideas  respecting  the  cause  of 
the  ascent  of  smoke,  and  consequently  tend  to  prevent 
the  progress  of  improvements  in  the  management  of 
fires.  The  experiment  just  mentioned  with  the  coloured 
water  is  very  striking  and  beautiful,  and  it  is  well  calcu- 
lated to  give  a  just  idea  of  the  cause  of  the  ascent  of 
smoke.  The  cold  water  in  the  jar,  which,  in  conse- 
quence of  its  superior  weight  or  density,  forces  the 
heated  and  rarefied  water  in  the  bottle  to  give  place  to 
it,  and  to  move  upwards  out  of  its  way,  may  represent 
the  cold  air  of  the  atmosphere,  while  the  rising  column 
of  coloured  water  will  represent  the  column  of  smoke 
which  ascends  from  a  fire. 

If  smoke  required  a  chimney  to  draw  it  upwards, 
how  happens  it  that  smoke  rises  from'  a  fire  which  is 
made  in  the  open  air,  where  there  is  no  chimney? 

If  a  tube,  open  at  both  ends,  and  of  such  a  length 
that  its  upper  end  be  below  the  surface  of  the  cold  water 
in  the  jar,  be  held  vertically  over  the  mouth  of  the 
bottle  which  contains  the  hot  coloured  water,  the  hot 
water  will  rise  up  through  it,  just  as  smoke  rises  in  a 
chimney. 

If  the  tube  be  previously  heated  before  it  is  plunged 
into  the  cold  water,  the  ascent  of  the  hot  coloured  water 
will  be  facilitated  and  accelerated,  in  like  manner  as 
smoke  is  known  to  rise  with  greater  facility  in  a  chimney 
which  is  hot,  than  in  one  in  which  no  fire  has  been  made 
for  a  long  time.  But  in  neither  of  these  cases  can  it, 
with  any  propriety,  be  said  that  the  hot  water  is  drawn 


Of  Ch  im  ney  Fireplaces.  537 

up  the  tube.  The  hotter  the  water  in  the  bottle  is,  and 
the  colder  that  in  the  jar,  the  greater  will  be  the  velocity 
with  which  the  hot  water  will  be  forced  up  through  the 
tube ;  and  the  same  holds  of  the  ascent  of  hot  smoke  in 
a  chimney.  When  the  fire  is  intense,  and  the  weather 
very  cold,  the  ascent  of  the  smoke  is  very  rapid ;  and 
under  such  circumstances  chimneys  seldom  smoke. 

As  the  cold  water  of  the  jar  immediately  surrounding 
the  bottle  which  contains  the  hot  water  will  be  heated 
by  the  bottle,  while  the  other  parts  of  the  water  in  the 
jar  will  remain  cold,  this  water  so  heated,  becoming 
specifically  lighter  than  that  which  surrounds  it,  will  be 
forced  upwards  ;  and  if  it  finds  its  way  into  the  tube  will 
rise  up  through  it  with  the  coloured  hot  water.  The 
warmed  air  of  a  room  heated  by  an  open  chimney  fire- 
place has  always  a  tendency  to  rise  (if  I  may  use  that  in- 
accurate expression),  and,  finding  its  way  into  the  chim- 
ney, frequently  goes  off  with  the  smoke. 

What  has  been  said  will,  I  flatter  myself,  be  sufficient 
to  explain  and  illustrate,  in  a  clear  and  satisfactory  man- 
ner, the  cause  of  the  ascent  of  smoke;  and  just  ideas 
upon  that  subject  are  absolutely  necessary  in  order  to 
judge,  with  certainty,  of  the  merit  of  any  scheme  pro- 
posed for  the  improvement  of  fireplaces,  or  to  take 
effectual  measures,  in  all  cases,  for  curing  smoking 
chimneys.  For,  though  the  perpetual  changes  and  alter- 
ations which  are  produced  by  accident,  whim,  and 
caprice,  do  sometimes  lead  to  useful  discoveries,  yet  the 
progress  of  improvement  under  such  guidance  must  be 
exceedingly  slow,  fluctuating,  and  uncertain. 

As  to  the  causes  of  the  smoking  of  chimneys,  they 
are  very  numerous  and  various ;  but  as  a  general  idea 
of  them  .may  be  acquired  from  what  has  already  been 


538  Of  Chimney  Fireplaces. 

said  upon  that  subject  in  various  parts  of  this  essay, 
and  as  they  may,  in  all  cases  (a  very  few  only  excepted), 
be  completely  remedied  by  making  the  alterations  in 
fireplaces  here  pointed  out,  I  do  not  think  it  necessary 
to  enumerate  them  all  in  this  place,  or  to  enter  into 
those  long  details  and  investigations  which  would  be 
required  to  show  the  precise  manner  in  which  each  of 
them  operates,  either  alone  or  in  conjunction  with  others. 

There  is,  however,  one  cause  of  smoking  chimneys 
which  I  think  it  is  necessary  to  mention  more  particu- 
larly. In  modern-built  houses,  where  the  doors  and 
windows  are  generally  made  to  close  with  such  accuracy 
that  no  crevice  is  left  for  the  passage  of  the  air  from 
without,  the  chimneys  in  rooms  adjoining  to  each  other, 
or  connected  by  close  passages,  are  frequently  found  to 
affect  each  other;  and  this  is  easy  to  be  accounted  for. 
When  there  is  a  fire  burning  in  one  of  the  chimneys,  as 
the  air  necessary  to  supply  the  current  up  the  chimney 
where  the  fire  burns  cannot  be  had  in  sufficient  quanti- 
ties from  without,  through  the  very  small  crevices  of 
the  doors  and  windows,  the  air  in  the  room  becomes 
rarefied,  not  by  heat,  but  by  subtraction  of  that  por- 
tion of  air  which  is  employed  in  keeping  up  the  fire,  or 
supporting  the  combustion  of  the  fuel,  and,  in  conse- 
quence of  this  rarefaction,  its  elasticity  is  diminished, 
and  being  at  last  overcome  by  the  pressure  of  the  ex- 
ternal air  of  the  atmosphere,  this  external  air  rushes  in- 
to the  room  by  the  only  passage  left  for  it,  namely,  by 
the  open  chimney  of  the  neighbouring  room ;  and  the 
flow  of  air  into  the  fireplace,  and  up  the  chimney  where 
the  fire  is  burning,  being  constant,  this  expense  of  air  is 
supplied  by  a  continued  current  down  the  other  chimney. 

If  an  attempt  be  made  to  light  fires  in  both. chimneys 


Of  Chimney  Fireplaces.  539 

at  the  same  time,  it  will  be  found  to  be  very  difficult  to 
get  the  fires  to  burn,  and  the  rooms  will  both  be  filled 
with  smoke. 

One  of  the  fires  —  that  which  is  made  in  the  chimney 
where  the  construction  of  the  fireplace  is  best  adapted 
to  facilitate  the  ascent  of  the  smoke ;  or,  if  both  fireplaces 
are  on  the  same  construction,  that  which  has  the  wind 
most  favourable,  or  in  which  the  fire  happens  to  be 
soonest  kindled  —  will  overcome  the  other,  and  cause 
its  smoke  to  be  beat  back  into  the  room  by  the  cold  air 
which  descends  through  the  chimney.  The  most  ob- 
vious remedy  in  this  case  is  to  provide  for  the  supply 
of  fresh  air  necessary  for  keeping  up  the  fires  by  open- 
ing a  passage  for  the  external  air  into  the  room  by  a 
shorter  road  than  down  one  of  the  chimneys ;  and  when 
this  is  done,  both  chimneys  will  be  found  to  be  effectu- 
ally cured. 

But  chimneys  so  circumstanced  may  very  frequently 
be  prevented  from  smoking,  even  without  opening  any 
new  passage  for  the  external  air,  merely  by  diminishing 
the  draught  (as  it  is  called)  up  the  chimneys ;  which 
can  best  be  done  by  altering  both  fireplaces  upon  the 
principles  recommended  and  fully  explained  in  the  fore- 
going chapters  of  this  essay. 

Should  the  doors  and  windows  of  a  room  be  closed 
with  so  much  nicety  as  to  leave  no  crevices  by  which  a 
supply  of  air  can  enter  sufficient  for  maintaining  the  fire, 
after  the  current  of  air  up  the  chimney  has  been  diminished  as 
much  as  possible  by  diminishing  the  throat  of  the  fireplace, 
in  that  case  there  would  be  no  other  way  of  preventing 
the  chimney  from  smoking  but  by  opening  a  passage  for 
the  admission  of  fresh  air  from  without;  but  this,  I 
believe,  will  very  seldom  be  found  to  be  the  case. 


540  Of  Chimney  Fireplaces. 

A  case  more  frequently  to  be  met  with  is,  where  cur- 
rents of  air  set  down  chimneys  in  consequence  of  a 
diminution  and  rarefaction  of  the  air  in  a  room,  occa- 
sioned by  the  doors  of  the  room  opening  into  passages 
or  courts  where  the  air  is  rarefied  by  the  action  of  some 
particular  winds.  In  such  cases  the  evil  may  be  reme- 
died, either  by  causing  the  doors  in  question  to  close 
more  accurately,  or  (which  will  be  still  more  effectual) 
by  giving  a  supply  of  air  to  the  passage  or  court  which 
wants  it  by  some  other  way. 

Where  the  top  of  a  chimney  is  commanded  by  high 
buildings,  by  cliffs,  or  by  high  grounds,  it  will  fre- 
quently happen,  in  windy  weather,  that  the  eddies 
formed  in  the  atmosphere  by  these  obstacles  will  blow 
down  the  chimney,  and  beat  down  the  smoke  into  the 
room.  This,  it  is  true,  will  be  much  less  likely  to  happen 
when  the  throat  of  the  chimney  is  contracted  and  prop- 
erly formed  than  when  it  is  left  quite  open,  and  the  fire- 
place badly  constructed ;  but  as  it  is  •possible  that  a  chim- 
ney may  be  so  much  exposed  to  these  eddies  in  very 
high  winds  as  to  be  made  to  smoke  sometimes  when  the 
wind  blows  with  violence  from  a  certain  quarter,  it  is 
necessary  to  show  how  the  effects  of  those  eddies  may 
be  prevented. 

Various  mechanical  contrivances  have  been  imagined 
for  preventing  the  wind  from  blowing  down  chimneys, 
and  many  of  them  have  been  found  to  be  useful ;  there 
are,  however,  many  of  these  inventions,  which,  though 
they  prevent  the  wind  from  blowing  down  the  chimney, 
are  so  ill-contrived  on  other  accounts  as  to  obstruct  the 
ascent  of  the  smoke,  and  do  more  harm  than  good. 

Of  this  description  are  all  those  chimney-pots  with 
flat  horizontal  plates  or  roofs  placed  upon  supporters 


Of  Chimney  Fireplaces.  541 

just  above  the  opening  of  the  pot ;  and  most  of  the 
caps  which  turn  with  the  wind  are  not  much  better.  One 
of  the  most  simple  contrivances  that  can  be  made  use 
of,  and  which  in  most  cases  will  be  found  to  answer  the 
purpose  intended  as  well  or  better  than  more  com- 
plicated machinery,  is  to  cover  the  top  of  the  chimney 
with  a  hollow  truncated  pyramid  or  cone,  the  diameter 
of  which  above,  or  opening  for  the  passage  of  the 
smoke,  is  about  10  or  n  inches.  This  pyramid,  or 
cone  (for  either  will  answer),  should  be  of  earthen- 
ware or  of  cast-iron ;  its  perpendicular  height  may 
be  equal  to  the  diameter  of  its  opening  above,  and  the 
diameter  of  its  opening  below  equal  to  three  times  its 
height.  It  should  be  placed  upon  the  top  of  the  chim- 
ney, and  it  may  be  contrived  so  as  to  make  a  handsome 
finish  to  the  brick-work.  Where  several  flues  come  out 
near  each  other,  or  in  the  same  stack  of  chimneys,  the 
form  of  a  pyramid  will  be  better  than  that  of  a  cone  for 
these  covers. 

The  intention  of  this  contrivance  is,  that  the  winds 
and  eddies  which  strike  against  the  oblique  surface  of 
these  covers  may  be  reflected  upwards,  instead  of  blow- 
ing down  the  chimney.  The  invention  is  by  no  means 
new,  but  it  has  not  hitherto  been  often  put  in  practice. 
As  often  as  I  have  seen  it  tried,  it  has  been  found  to  be 
of  use;  I  cannot  say,  however,  that  I  was  ever  obliged 
to  have  recourse  to  it,  or  to  any  similar  contrivance  ;  and 
if  I  forbear  to  enlarge  upon  the  subject  of  these  inven- 
tions, it  is  because  I  am  persuaded  that  when 'chimneys  . 
are  properly  constructed  in  the  neighbourhood  of  the  fire- 
place, little  more  will  be  necessary  to  be  done  at  the  top 
of  the  chimney  than  to  leave  it  open. 

I   cannot  conclude  this  essay  without  again  recom- 


542  Of  Chimney  Fireplaces. 

mending,  in  the  strongest  manner,  a  careful  attention  to 
the  management  of  fires  in  open  chimneys  ;  for  not  only 
the  quantity  of  heat  produced  in  the  combustion  of 
fuel  depends  much  on  the  manner  in  which  the  fire  is 
managed,  but  even  of  the  heat  actually  generated  a 
very  small  part  only  will  be  saved,  or  usefully  em- 
ployed, when  the  fire  is  made  in  a  careless  and  slovenly 
manner. 

In  lighting  a  coal  fire,  more  wood  should  be  employed 
than  is  commonly  used,  and  fewer  coals ;  and  as  soon 
as  the  fire  burns  bright,  and  the  coals  are  well  lighted, 
and  not  before,  more  coals  should  be  added  to  increase 
the  fire  to  its  proper  size.* 

The  enormous  waste  of  fuel  in  London  may  be  esti- 
mated by  the  vast  dark  cloud  which  continually  hangs 
over  this  great  metropolis,  and  frequently  overshadows 

*  Kindling-balls,  composed  of  equal  parts  of  coal,  charcoal,  and  clay,  the  two 
former  reduced  to  a  fine  powder,  well  mixed  and  kneaded  together  with  the  clay 
moistened  with  water,  and  then  formed  into  balls  of  the  size  of  hens'  eggs,  and 
thoroughly  dried,  might  be  used  with  great  advantage  instead  of  wood  for  kindling 
fires.  These  kindling-balls  may  be  made  so  inflammable  as  to  take  fire  in  an  instant, 
and  with  the  smallest  spark,  by  dipping  them  in  a  strong  solution  of  nitre  and  then 
drying  them  again;  and  they  would  neither  be  expensive  nor  liable  to  be  spoiled  by 
long  keeping.  Perhaps  a  quantity  of  pure  charcoal,  reduced  to  a  very  fine  powder 
and  mixed  with  the  solution  of  nitre  in  which  they  are  dipped,  would  render  them 
still  more  inflammable. 

I  have  often  wondered  that  no  attempts  should  have  been  made  to  improve  the 
fires  which  are  made  in  the  open  chimneys  of  elegant  apartments,  by  preparing  the 
fuel ;  for  nothing  surely  was  ever  more  dirty,  inelegant,  and  disgusting  than  a  com- 
mon coal  fire. 

Fire-balls,  of  the  size  of  goose-eggs,  composed  of  coal  and  charcoal  in  powder, 
mixed  up  with  a  due  proportion  of  wet  clay,  and  well  dried,  would  make  a  much 
more  cleanly,  and  in  all  respects  a  pleasanter,  fire  than  can  be  made  with  crude  coals  ; 
and  I  believe  would  not  be  more  expensive  fuel.  In  Flanders  and  in  several  parts  of 
Germany,  and  particularly  in  the  Duchies  of  Juliers  and  Bergen,  where  coals  are  used 
as  fuel,  the  coals  are  always  prepared  before  they  are  used,  by  pounding  them  to  a 
powder,  and  mixing  them  up  with  an  equal  weight  of  clay,  and  a  sufficient  quantity 
of  water  to  form  the  whole  into  a  mass  which  is  kneaded  together  and  formed  into 
cakes  5  which  cakes  are  afterwards  well  dried  and  kept  in  a  dry  place  for  use.  And 


Of  Chimney  Fireplaces.  543 

the  whole  country,  far  and  wide ;  for  this  dense  cloud  is 
certainly  composed  almost  entirely  of  unconsumed  coat, 
which,  having  stolen  wings  from  the  innumerable  fires 
of  this  great  city,  has  escaped  by  the  chimneys,  and  con- 
tinues to  sail  about  in  the  air,  till,  having  lost  the  heat 
which  gave  it  volatility,  it  falls  in  a  dry  shower  of  ex- 
tremely fine  black  dust  to  the  ground,  obscuring  the  at- 
mosphere in  its  descent,  and  frequently  changing  the 
brightest  day  into  more  than  Egyptian  darkness. 

I  never  view  from  a  distance,  as  I  come  into  town, 
this  black  cloud  which  hangs  over  London,  without 
wishing  to  be  able  to  compute  the  immense  number  of 
caldrons  of  coals  of  which  it  is  composed ;  for,  could 
this  be  ascertained,  I  am  persuaded  so  striking  a  fact 
would  awaken  the  curiosity  and  excite  the  astonishment 
of  all  ranks  of  the  inhabitants,  and  perhaps  turn  their 

it  has  been  found  by  long  experience,  that  the  expense  attending  this  preparation  is 
amply  repaid  by  the  improvement  of  the  fuel.  The  coals,  thus  mixed  with  clay,  not 
only  burn  longer,  but  give  much  more  heat  than  when  they  are  burned  in  their  crude 
state. 

It  will  doubtless  appear  extraordinary  to  those  who  have  not  considered  the  subject 
with  some  attention,  that  the  quantity  of  heat  produced  in  the  combustion  of  any 
given  quantity  of  coals  should  be  increased  by  mixing  the  coals  with  clay,  which  is 
certainly  an  incombustible  body ;  but  the  phenomenon  may,  I  think,  be  explained  in 
a  satisfactory  manner. 

The  heat  generated  in  the  combustion  of  any  small  particle  of  coal  existing  under 
two  distinct  forms,  namely,  in  that  which  is  combined  with  the  flame  and  smoke 
which  rise  from  the  fire,  and  which,  if  means  are  not  found  to  stop  it,  goes  off  im- 
mediately by  the  chimney  and  is  lost,  and  the  radiant  heat  which  is  sent  off  from  the 
fire,  in  all  directions,  in  right  lines;  I  think  it  reasonable  to  conclude,  that  the  parti- 
cles of  clay,  which  are  surrounded  on  all  sides  by  the  flame,  arrest  a  part  at  least  of  the 
combined  heat,  and  prevent  its  escape;  and  this  combined  heat  so  arrested,  heating 
the  clay  red-hot,  is  retained  in  it,  and,  being  changed  by  this  operation  to  radiant  heat, 
is  afterwards  emitted,  and  may  be  directed  and  employed  to  useful  purposes. 

In  composing  fire-balls,  I  think  it  probable  that  a  certain  proportion  of  chaff— of 
straw  cut  very  fine,  or  even  of  saw-dust  —  might  be  employed  with  great  advantage.  1 
wish  those  who  have  leisure  would  turn  their  thoughts  to  this  subject,  for  I  am  per- 
suaded that  very  important  improvements  would  result  from  a  thorough  investigation 
of  it. 


544  Of  Chimney  Fireplaces. 

minds  to  an  object  of  economy  to  which  they  have  hith- 
erto paid  little  attention. 

Conclusion. 

Though  the  saving  of  fuel  which  will  result  from  the 
improvements  in  the  forms  of  chimney  fireplaces^  here 
recommended,  will  be  very  considerable,  yet  I  hope  to 
be  able  to  show  in  a  future  essay  that  still  greater 
savings  may  be  made,  and  more  important  advantages 
derived,  from  the  introduction  of  improvements  I  shall 
propose  in  kitchen  fireplaces. 

I  hope,  likewise,  to  be  able  to  show  in  an  essay  on 
cottage  fireplaces,  which  I  am  now  preparing  for  publica- 
tion, that  three  quarters^  at  least,  of  the  fuel  which  cot- 
tagers now  consume  in  cooking  their  victuals  and  in 
warming  their  dwellings,  may  with  great  ease,  and  with- 
out any  expensive  apparatus,  be  saved. 

[This  paper  is  printed  from  the  English  edition  of  Rumford's 
Essays,  Vol.  I,  pp.  305-387.] 


546  Of  Chimney  Fireplaces, 


EXPLANATION    OF   THE    FIGURES. 


PLATE    VIII. 
FIG.   i. 


The  plan  of  a  fireplace  on  the  common  construction. 
A  B,  the  opening  of  the  fireplace  in  front. 
C  D,  the  back  of  the  fireplace. 
A  C  and  B  D,  the  covings. 

See  page  523. 


FIG.   2. 


This  figure  shows  the  elevation,  or  front  view,  of  a 
fireplace  on  the  common  construction.     See  page  523. 


PLATE    VIII. 


Fig-,1. 


548  Of  Chimney  Fireplaces. 


PLATE    IX. 
FIG.   3. 

This  figure  shows  how  the  fireplace  represented  by 
the  Fig.  i  is  to  be  altered,  in  order  to  its  being  im- 
proved. 

A  B  is  the  opening  in  front,  C  D  the  back,  and  A  C 
and  B  D  the  covings  of  the  fireplace  in  its  original 
state. 

a  b  its  opening  in  front,  /  k  its  back,  and  a  i  and  b  k 
its  covings  after  it  has  been  altered  ;  e  is  a  point  upon 
the  hearth  upon  which  a  plumb  suspended  from  the 
middle  of  the  upper  part  of  the  breast  of  the  chimney 
falls.  The  situation  for  the  new  back  is  ascertained  by 
taking  the  line  ef  equal  to  four  inches.  The  new  back 
and  covings  are  represented  as  being  built  of  bricks,  and 
the  space  between  these  and  the  old  back  and  covings  as 
being  filled  up  with  rubbish.  See  page  523. 

FIG.  4. 

This  figure  represents  the  elevation  or  front  view  of 
the  fireplace  (Fig.  3)  after  it  has  been  altered.  The 
lower  part  of  the  doorway  left  for  the  chimney-sweeper 
is  shown  in  this  figure  by  white  dotted  lines.  See  page 

525- 


PLATE    IX. 


1 I I * 


Feet. 


55°  Of  Chimney  Fireplaces. 


PLATE    X. 
FIG.    5. 

This  figure  shows  the  section  of  a  chimney  fireplace 
and  of  a  part  of  the  canal  of  the  chimney  on  the  com- 
mon construction. 

a  b  is  the  opening  in  front ;  b  c  the  depth  of  the  fire- 
place at  the  hearth  ;  d  the  breast  of  the  chimney. 

d  e^  the  throat  of  the  chimney,  and  d /,  g  e,  a  part  of 
the  open  canal  of  the  chimney. 

FIG.  6. 

Shows  a  section  of  the  same  chimney  after  it  has  been 
altered. 

k  I  is  the  new  back  of  the  fireplace ;  /  /  the  tile  or 
stone  which  closes  the  doorway  for  the  chimney-sweeper; 
di  the  throat  of  the  chimney,  narrowed  to  four  inches; 
#,  the  mantle,  and  £,  the  new  wall  made  under  the  man- 
tle, to  diminish  the  height  of  the  opening  of  the  fireplace 
in  front. 

N.  B. — These  two  figures  are  sections  of  the  same 
chimney  which  is  represented  in  each  of  the  four  pre- 
ceding figures. 


PL  ATI.    X 


Fijr.6. 


552  Of  Chimney  Fireplaces. 


PLATE    XI. 

FIG.   7. 

This  figure  represents  the  ground  plan  of  a  chimney 
fireplace  in  which  the  grate  is  placed  in  a  niche,  and  in 
which  the  original  width  A  B  of  the  fireplace  is  consid- 
erably diminished. 

a  b  is  the  opening  of  the  fireplace  in  front  after  it  has 
been  altered,  and  d  is  the  back  of  the  niche  in  which  the 
grate  is  placed.  See  page  527. 

FIG.  8. 

Shows  a  front  view  of  the  same  fireplace  after  it  has 
been  altered ;  where  may  be  seen  the  grate,  and  the 
doorway  for  the  chimney-sweeper.  See  page  527. 

FIG.  9. 

Shows  a  section  of  the  same  fireplace,  c  d  e  being  a 
section  of  the  niche,  g  the  doorway  for  the  chimney- 
sweeper, closed  by  a  piece  of  firestone,  and  /  the  new 
wall  under  the  mantle,  by  which  the  height  of  the  open- 
ing of  the  fireplace  in  front  is  diminished.  See  page 
527. 


PLATE    XI, 


Scale  y[. 


f         1 


554  Of  Chimney  Fireplaces. 


PLATE    XII. 
FIG.   10. 


This  figure  shows  how  the  covings  are  to  be  placed 
when  the  front  of  the  covings  (a  and  ^)  do  not  come  so 
far  forward  as  the  front  of  the  opening  of  the  fireplace, 
or  the  jambs  (A  and  B).  See  page  528. 


FIG.    ii. 


This  figure  shows  how  the  width  and  obliquity  of  the 
covings  are  to  be  accommodated  to  the  width  of  the  back 
of  a  fireplace,  in  cases  where  it  is  necessary  to  make  the 
back  very  wide.  See  page  529. 


PLATE    XII. 


Pig.10. 


Fig.ll. 


5 5 5  Of  Chimney  Fireplaces, 


PLATE    XIII. 

FIG.    12. 

This  figure  shows  how  an  instrument  called  a  bevel 
(m  »),  useful  in  laying  out  the  work,  in  altering  chimney 
fireplaces,  may  be  constructed.  See  page  530. 

FIG.   13. 

This  shows  how,  when  the  breast  of  a  chimney  (d)  is 
too  high,  it  may  be  brought  down  by  means  of  a  wall 
(h)  placed  under  the  mantle,  and  a  coating  of  plaster, 
which  in  this  figure  is  represented  by  the  part  marked 
by  dots.  See  page  532. 

FIG.   14. 

This  shows  how  the  breast  of  a  chimney  may  be 
brought  down  merely  by  a  coating  of  plaster.  See  page 

533- 


PLATE    XIII. 


Tig".  13. 


SUPPLEMENTARY    OBSERVATIONS 

CONCERNING 

CHIMNEY  FIREPLACES. 


OBSERVATIONS     CONCERNING     OPEN     CHIMNEY    FIRE- 
PLACES. 

An  Account  of  various  Faults  that  have  been  committed  by 
Workmen,  in  England,  who  have  been  employed  in  altering 
Chimney  Fireplaces,  and  fitting  them  up  according  to  the 
Method  recommended  by  the  Author,  in  his  Fourth  Essay. 

—  Consequences  which  have  resulted  from  these  Mistakes. 

—  Necessity  of  adhering  strictly,  and  without  Deviation,  to 
the  Directions  which  have  been  given.  —  Those  Particulars 
are  pointed  out  in  which  Workmen  are  most  liable  to  fail. 

I  WAS  much  flattered  on  my  return  to  England,  in 
September,  1798,  after  an  absence  of  two  years,  to 
find  that  the  improvements  in  the  construction  of  chim- 
ney fireplaces,  which  I  had  recommended  in  my  Fourth 
Essay,  published  in  London  in  the  beginning  of  the 
year  1796,  were  coming  into  use  in  various  parts  of  the 
country;  and  I  have  since  taken  a  good  deal  of  pains 
to  find  out  how  they  have  answered,  and  what  faults 
and  imperfections  have  been  discovered  in  them.  And 
as  the  information  I  have  obtained  by  these  inquiries 
has  enabled  me  to  make  several  remarks  and  observa- 


560  Of  Chimney  Fireplaces. 

tions  relative  to  the  construction  and  management  of 
these  fireplaces,  that  may  be  of  use  to  those  who  have  in- 
troduced them,  or  may  be  desirous  of  introducing  them, 
I  feel  it  to  be  my  duty  to  lay  them  before  the  public. 

It  has  been  objected  to  these  fireplaces,  that  they 
sometimes  occasion  dust  and  ashes  to  come  into  the 
room  when  the  fire  is  stirred.  I  have  examined  several 
fireplaces  said  to  have  been  fitted  up  on  my  principles, 
that  have  certainly  had  that  fault;  but  I  have  common- 
ly, I  might  say  invariably,  found,  that  their  imperfections 
have  arisen  from  faults  in  their  construction.  Either 
the  grate  has  been  brought  out  too  far  into  the  room,  or 
the  opening  of  the  fireplace  in  front  has  been  left  too 
wide  or  too  high,  or  the  workman  has  neglected  to 
lower  and  to  round  off  the  breast  of  the  chimney,  or, 
what  I  have  often  found  to  be  the  case,  several  of  these 
faults  have  existed  together,  in  the  same  fireplace. 

When  the  throat  of  a  chimney  is  situated  very  high 
up  above  the  mantle,  and  especially  when  the  mantle 
and  breast  of  the  chimney,  or  the  wall  that  reposes  on 
the  mantle,  are  very  thin,  workmen  who  are  employed 
to  alter  chimneys,  setting  about  the  work  with  their 
minds  strongly  prepossessed  with  what  they  consider  as 
the  leading  principle 'in  the  construction  of  these  fireplaces, 
namely,  that  the  throat  of  the  chimney  should  not  be 
more  than  four  inches  wide,  they  are  very  apt  to  bring 
the  grate  too  far  forward.  In  dropping  their  plumb- 
line  from  the  breast  of  the  chimney,  they  do  not  reach 
up  high  enough  into  the  chimney,  but  take  a  part  of  the 
breast,  where  it  still  goes  on  to  slope  backwards,  for  the 
bottom  of  the  perpendicular  canal  of  the  chimney. 
They  also  very  often  commit  another  fault,  not  less 
essential,  and  that  has  the  same  tendency,  in  neglecting 


Of  Chimney  Fireplaces.  56 1 

to  bring  down  the  throat  of  the  chimney  nearer  to  the  fire, 
when  it  happens  to  be  situated  too  high. 

This  I  have  not  only  recommended  in  my  Essay  on 
Chimney  Fireplaces,  but  have  given  the  most  particular 
directions  how  it  is  to  be  done  (see  page  531),  and,  to 
mark  the  importance  of  the  object  still  more  strongly, 
have  accompanied  those  directions  by  an  engraving. 

It  is  indeed  a  very  important  point,  that  the  throat 
of  the  chimney  should  be  near  the  fire,  and  it  should 
always  be  carefully  attended  to.  It  is  likewise  very  im- 
portant to  " round  off  the  breast  of  the  chimney"  though 
this,  I  find,  is  very  often  entirely  neglected,  even  by 
workmen  who  have  had  much  practice  in  the  construc- 
tion of  the  fireplaces  I  have  recommended. 

The  breast  of  a  chimney  should  always  be  rounded 
off  in  the  neatest  manner  possible,  beginning  from  the 
very  front  of  the  lower  part  of.  the  mantle,  and  ending 
at  the  narrowest  part  of  the  throat  of  the  chimney, 
where  the  breast  ends  in  the  front  part  of  the  perpen- 
dicular canal  of  the  chimney.  If  the  under  surface  of 
the  mantle  is  flat  and  wide,  it  will  be  impossible  to 
round  off  the  breast  properly ;  and  that  circumstance 
alone  renders  it  indispensably  necessary,  in  those  cases, 
to  alter  the  mantle,  or  to  run  under  it  a  thinner  piece  of 
stone,  or  a  thin  wall  of  bricks,  supported  on  an  iron 
bar,  in  order  that  the  breast  of  the  chimney  may  be 
brought  to  be  of  the  proper  form,  and  the  throat  of  the 
chimney  may  be  brought  into  its  proper  situation. 

If  the  under  side  of  the  mantle  be  left  broad  and  flat, 
it  is  easy  to  perceive  that  the  cloud  of  dust  or  light 
ashes  that  rises  from  a  coal  fire  nearly  burned  out  when 
it  is  violently  stirred  about  with  a  poker,  striking  per- 
pendicularly against  this  flat  part  of  it,  must  unavoid- 

voi..  ii.  36 


562  Of  Chimney  Fireplaces. 

ably  be  beat  back  into  the  room  ;  but  when  the  breast 
of  the  chimney  is  properly  rounded  off,  the  ascending 
cloud  of  dust  and  smoke  more  easily  finds  its  way  into 
the  throat  of  the  chimney,  and  is  even  directed  and 
assisted  in  some  measure  by  the  warm  air  of  the  room 
that  gets  under  the  mantle,  and  is  going  the  same  way. 

Another  very  common  fault  that  I  have  observed  in 
chimney  fireplaces,  that  have  been  altered  on  what  have 
been  called  my  principles,  and  which  has  a  direct  ten- 
dency to  bring  dust,  and  even  smoke,  into  the  room,  is 
the  sloping  of  the  covings  too  much,  and  leaving  the 
opening  of  the  fireplace  in  front  too  wide.  I  have  said, 
in  my  Essay  on  Chimney  Fireplaces,  that  where  chimneys 
are  well  constructed  and  well  situated,  and  have  never 
been  apt  to  smoke,  in  altering  them  the  covings  may  be 
placed  at  an  angle  of  135  degrees  with  the  back;  but  I 
have  expressly  said  that  they  should  never  exceed  that 
angle,  and  have  stated  at  large  the  bad  consequences 
that  must  follow  from  making  the  opening  of  a  fireplace 
very  wide,  when  its  depth  is  very  shallow  (see  page 
510).  I  have  also  expressly  said  (page  530),  that, 
for  chimneys  that  are  apt  to  smoke,  the  covings  should 
be  placed  less  obliquely^  in  respect  to  the  back,  than  in 
others  that  have  not  that  fault.  But  most  of  the  work- 
men who  have  altered  chimneys  seem  to  have  paid  little 
attention  to  these  distinctions,  and  I  have  frequently 
found,  and  sometimes  in  fireplaces  that  have  been  re- 
markably shallow,  that  the  covings  have  been  placed  at 
an  angle  even  more  oblique  than  that  above  mentioned. 

Another  cause  that  sometimes  has  considerable  effect 
in  bringing  dust  and  smoke  into  rooms,  from  the  fires 
that  are  made  in  them,  is  the  great  nicety  with  which  the 
doors  and  windows  are  fitted  in  their  frames,  which  pre- 


Of  Chimney  Fireplaces.  563 

vents  a  sufficient  quantity  of  fresh  air  from  coming  into 
the  room  to  supply  a  brisk  current  up  the  chimney.  It 
is,  however,  evident,  that  all  the  alterations  in  fireplaces 
on  the  common  construction,  that  have  been  recom- 
mended in  order  to  improve  them,  must  tend  directly 
and  very  powerfully  to  lessen  this  evil;  but  nothing  will 
so  completely  remedy  it  as  lowering  the  mantle,  and 
diminishing  the  width  of  the  fireplace. 

How  many  fireplaces  in  close  rooms  have  been  cured 
completely  of  throwing  puffs  of  smoke  and  dust  into 
the  room,  merely  by  placing  a  register  stove  in  them  ! 
But  there  is  surely  nothing  peculiar  to  a  register-stove 
that  could  enable  it  to  perform  such  a  cure,  but  merely 
as  it  serves  to  diminish  the  width  and  height  of  the 
opening  of  the  fireplace ;  and  how  much  easier  could 
this  be  done  with  marble,  or  other  stone,  or  with  bricks 
and  mortar,  plastered  over  and  incrusted  in  front  with 
proper  ornaments  in  stucco,  or  in  artificial  stone  ! 

I  am  the  more  anxious  that  something  of  this  sort 
should  be  introduced,  as  the  openings  of  chimney  fire- 
places are  in  general  certainly  too  wide  and  too  high, 
and  as  I  am  convinced  that  there  is  no  way  of  reducing 
them  to  a  proper  size,  that  would  be  so  cheap,  or  more 
effectual,  or  that  could  be  made  more  ornamental. 

Those  who  are  fond  of  the  glitter  of  polished  steel, 
and  have  no  objection  to  the  expense  of  it,  or  to  the 
labour  that  is  required  to  keep  it  bright,  may  surround 
their  fireplaces  in  front  with  a  border  of  it,  for  there  it 
will  do  no  harm,  and  may  use  grates  and  fenders  of  the 
most  exquisite  workmanship;  but  if  they  wish  to  have 
a  pleasant,  cheerful,  and  economical  fire,  the  covings  of 
their  fireplaces  must  be  placed  obliquely,  and  they  must 
not  be  constructed  of  metal ;  and  if  the  sides  and  back 


564  Of  Chimney  Fir ep  faces. 

of  the  grate  be  constructed  of  fire-bricks  instead  of  iron, 
the  fire  will  burn  still  brighter,  and  will  send  off  consid- 
erably more  radiant  heat  into  the  room. 

I  have  abundant  reason  to  think,  that  if,  in  construct- 
ing or  altering  chimney  fireplaces,  the  rules  laid  down  in 
my  essay  on  that  subject  are  strictly  adhered  to,  chim- 
neys so  fitted  up  will  very  seldom  be  found  either  to 
smoke,  or  to  throw  out  dust  into  the  room  ;  and  should 
they  be  found  to  have  either  of  these  faults,  there  is  a 
remedy  for  the  evil,  as  effectual  as  it  is  simple  and  ob- 
vious :  Bring  down  the  mantle  and  the  throat  of  the  chim- 
ney lower ;  and  if  it  should  be  found  necessary,  reduce  the 
width  of  the  opening  of  the  fireplace  in  front,  and  diminish 
obliquity  of  the  covings. 

These  alterations  will  certainly  be  effectual  to  prevent 
either  smoke  or  dust  from  coming  into  the  room  when 
there  is  a  fire  burning  in  the  grate  ;  but  it  sometimes  hap- 
pens, and  indeed  not  unfrequently,  that  dust  and  soot 
are  drawn  down  a  chimney  in  which  there  is  no  fire,  to 
the  great  annoyance  of  those  who  are  in  the  room,  and 
to  the  great  damage  of  the  furniture.  When  this  hap- 
pens, it  is  commonly  occasioned  by  a  very  strong 
draught  up  another  chimney,  in  which  there  is  afire,  in  an 
adjoining  room  ;  and  when  that  is  the  case,  the  most 
simple  remedy  is  to  alter  that  other  chimney,  and,  con- 
structing its  fireplace  on  good  principles,  to  reduce  its 
throat  to  reasonable  dimensions.  But  if  the  passage  of 
the  air  down  a  chimney  in  which  there  is  no  fire  is  occa- 
sioned by  strong  eddies  of  wind,  there  is  no  remedy  for 
that  evil  but  placing  a  chimney-pot,  of  a  peculiar  con- 
struction, on  the  top  of  the  chimney,  which  shall  coun- 
teract the  effect  of  those  eddies ;  or  by  closing  up  the 
throat  of  the  chimney  occasionally,  by  a  door  made  for 
that  purpose  of  sheet-iron. 


Of  Chimney  Fireplaces.  565 

If  the  doorway  that  is  left  in  the  back  of  the  fireplace 
for  giving  a  passage  to  the  chimney-sweeper,  instead  of 
being  closed  with  a  tile,  or  with  a  flat  piece  of  stone,  set 
in  a  groove  made  to  receive  it,  according  to  the  direc- 
tions given  in  my  Fourth  Essay,  be  closed  with  a  flat 
piece  of  cast-iron,  or  of  plate-iron,  fixed  at  its  lower 
end,  to  the  lower  end  of  the  doorway,  by  a  hinge,  or 
movable  on  two  gudgeons,  —  this  plate  may  easily  be  so 
contrived  as  to  serve  occasionally  as  a  register  or  door 
for  diminishing  or  closing  the  throat  of  the  chimney. 

As  this  plate,  situated  at  tht  back  part  of  the  chimney, 
could  not  produce  any  of  those  bad  effects  that  have 
with  reason  been  attributed  to  the  registers  of  common 
register-stoves  (which  are  placed  on  the  breast  of  the 
chimney),  it  appears  to  me  to  be  very  probable,  that  it 
would  be  found  useful  as  a  register  for  occasionally 
altering  the  size  of  the  throat  of  the  chimney,  and  regu- 
lating its  draught,  as  well  as  for  occasionally  closing  up 
that  passage  entirely.  It  would  certainly  be  worth  while 
to  try  the  experiment* 

Before  I  quit  this  subject,  I  must  mention  another 
fault,  which  workmen  employed  in  altering  chimney  fire- 
places that  are  furnished  with  grates  or  stoves  with 
sloping  backs  are  very  apt  to  make.  They  leave  the 
back  of  the  grate  in  its  place,  and  instead  of  carrying  up 
the  back  of  the  fireplace  perpendicularly  from  the  bottom 
of  the  grate,  they  first  begin  to  carry  it  up  perpendicu- 
larly from  the  top  of  the  iron  plate  that  forms  the  back 
of  the  grate ;  and  as  this  plate  not  only  slopes  back- 
wards considerably,  but  rises  several  inches  above  the 

*  Since  the  introduction  of  the  cottage  and  gridiron  grates,  this  contrivance  has 
come  into  very  general  use,  and  experience  has  shown  it  to  be  extremely  useful.  I 
would  strongly  recommend  it  to  those  who  fit  up  chimney  fireplaces  on  these  princi- 
ples, never  to  omit  this  register ;  it  costs  a  mere  trifle,  and  is  very  useful  on  many 

accounts. 


566  Of  Chimney  Fireplaces. 

level  of  the  upper  bar  of  the  grate,  this  necessarily 
throws  the  fire  very  far  into  the  room.  This  tends  to 
bring  both  smoke  and  dust  into  the  room,  not  only  be- 
cause it  brings  the  fire  too  far  forward,  but  also  because 
it  occasions  the  air  of  the  room,  that  slips  in  by  the 
sides  of  the  covings,  to  get  behind  the  current  of  smoke 
that  rises  perpendicularly  from  the  fire,  which  air  fre- 
quently crowds  the  smoke  forward,  and  causes  it  to 
strike  against  the  mantle.  This  is  a  great  fault,  and  I 
am  sorry  to  say  that  I  have  found  it  very  common  in 
many  parts  of  England,  where  attempts  have  been  made 
to  introduce  the  fireplaces  I  have  recommended.  Where 
grates  with  sloping  backs  are  used  in  fitting  up  these  fire- 
places, these  backs  must  either  be  taken  quite  away  or 
bricked  up,  and  the  new  back  part,  or  back  wall  of  the 
fireplace,  must  be  made  to  serve  as  a  back  for  the  grate, 
against  which  the  burning  fuel  is  laid. 

As  I  am  giving  an  account  of  the  mistakes  that  have 
been  made  by  some  of  those  who  have  been  employed 
in  fitting  up  chimney  fireplaces  on  the  principles  I  have 
publicly  recommended,  it  will  naturally  be  expected  that 
I  should  take  some  notice  of  those  numerous  improve- 
ments that  have  been  announced  to  the  public,  said  to 
have  been  made  in  stoves,  grates,  etc.,  to  which  adver- 
tisers in  the  newspapers  have  thought  proper  to  affix 
my  name.  As  I  am"  extremely  anxious  not  to  injure 
any  man,  either  in  his  reputation  for  ingenuity,  or  in 
his  trade,  or  in  any  other  way,  I  shall  not  say  one  word 
more  on  this  subject  than  what  I  feel  it  to  be  my  duty 
to  the  public  to  declare,  namely,  that  I  am  not  the  in- 
ventor of  any  of  those  stoves  or  grates  that  have  been 
offered  to  the  public  for  sale  under  my  name. 

Having  mentioned  the  inconveniences  that  sometimes 


Of  Chimney  Fireplaces.  567 

arise  from  doors  and  windows  being  fitted  to  their 
frames  with  so  much  nicety  as  not  to  give  a  sufficient 
passage  to  air  from  without  to  get  into  the  room  to 
supply  the  current  up  the  chimney,  which  must  always 
exist  when  a  fire  is  burning  in  the  room,  I  embrace  this 
opportunity  of  mentioning  a  contrivance  for  remedying 
this  defect,  which  I  am  persuaded  would  not  only  be 
found  most  effectual  for  that  purpose,  but  would  at  the 
same  time  contribute  very  essentially  to  rendering  dwell- 
ing-houses more  salubrious  and  more  comfortable,  by 
facilitating  the  means  of  warming  them  more  equally 
and  ventilating  them  more  easily  and  more  effectually. 

In  building  a  house,  an  air-canal^  about  twelve  or 
fifteen  inches  square,  in  the  clear,  and  open  at  both 
ends,  may  be  constructed  in  or  near  the  centre  of  each 
stack  of  chimneys;  and  two  branches  from  this  air- 
canal,  both  furnished  with  registers,  may  open  into  each 
of  the  adjoining  rooms,  —  one  of  these  branches  opening 
into  the  fireplace,  just  under  the  grate,  and  the  other 
over  the  fireplace,  and  near  the  top  of  the  room,  or  just 
under  the  ceiling.  Each  of  these  branches  should  be 
about  four  inches  square,  in  the  clear ;  and  to  prevent 
the  uncouth  appearance  of  the  open  mouth  of  that  which 
opens  into  the  room  over  the  fireplace,  it  may  be  masked 
by  a  medallion,  a  picture,  or  any  other  piece  of  orna- 
mental furniture  proper  for  that  use,  placed  before  it  at 
the  distance  of  one  or  two  inches  from  the  side  or  wall 
of  the  room. 

The  bottom  of  this  air-tube  should  reach  to  the 
ground,  where  it  should  communicate  freely  with  the 
open  air  of  the  atmosphere;  but  it  should  not  rise  quite 
so  high  as  the  chimneys  (or  canals  for  carrying  off  the 
smoke)  are  carried  up,  but  should  end  (by  lateral  open- 


568  Of  Chimney  Fireplaces. 

ings,  communicating  with  the  air  of  the  atmosphere) 
immediately  above  the  roof  of  the  house. 

If  this  air-tube  be  situated  in  the  middle  of  a  build- 
ing, it  is  evident  that  a  horizontal  canal  or  tube  of 
communication  must  be  carried  from  its  lower  orifice  to 
some  open  place  without  the  building,  in  order  to  estab- 
lish a  free  circulation  of  fresh  air,  both  upwards  and 
downwards,  in  the  air-tube.  I  say  both  upwards  and 
downwards,  for  sometimes  the  current  of  air  in  the  tube 
will  be  found  to  set  upwards,  and  sometimes  down- 
wards. Its  direction  will  depend  on  the  winds  that  hap- 
pen to  prevail,  or  rather  on  the  eddies  they  occasion  in 
the  air  out  of  doors  in  the  neighbourhood  of  the  build- 
ings ;  and  it  is  no  small  advantage"  that  will  arise  from 
leaving  both  ends  of  the  air-tube  open,  that  the  tube 
will  always  be  supplied  with  a  sufficiency  of  air,  what- 
ever eddies  the  winds  may  occasion.  It  is  easy  to  per- 
ceive how  powerfully  this  must  operate  to  prevent 
those  puffs  of  smoke  which,  in  high  winds,  are  fre- 
quently thrown  into  some  rooms  by  the  eddies,  and  the 
partial  rarefactions  of  the  air  that  they  occasion  ;  but 
this  is  far  from  being  the  only  or  the  most  important 
of  the  advantages  that  will  be  derived  from  this  air-tube. 
Those  who  consider  what  an  immense  quantity  of  air  is 
required  to  supply  the  current  that  sets  up  the  chimney 
of  an  open  fireplace,  where  there  is  a  fire  burning,  must 
perceive  what  an  enormous  loss  of  heat  there  must  be, 
when  all  this  expense  of  air  is  supplied  by  the  warmed 
air  of  the  room,  and  that  all  this  warmed  air  is  necessa- 
rily and  constantly  replaced  by  the  cold  air  from  with- 
out, which  finds  its  way  into  the  room  by  the  crevices 
of  the  doors  and  windows.  But  all  this  waste  of  heat, 
or  any  part  of  it,  at  pleasure,  may  be  prevented  by  the 


Of  Chimney  Fireplaces.  569 

scheme  proposed  ;  for  if  the  air  necessary  to  the  combus- 
tion of  the  fuel,  and  to  the  supplying  of  the  current  up 
the  chimney,  be  furnished  by  the  air-tube,  the  warmed 
air  in  the  room  will  remain  in  its  place  ;  and  as  this  will 
in  a  great  measure  prevent  the  cold  currents  from  the 
crevices  of  the  door  and  windows,  the  heat  in  the  room 
will  be  the  more  equable,  and  consequently  the  more 
wholesome  and  agreeable  on  that  account. 

But  there  are,  I  am  told,  persons  in  this  country, 
who  are  so  fond  of  seeing  what  is  called  a  great  roaring 
fire,  that  even  with  its  attendant  inconveniences,  of 
roasting  and  freezing  opposite  sides  of  the  body  at  the 
same  time,  they  prefer  it  to  the  genial  and  equable 
warmth  which  a  smaller  fire,  properly  managed,  may  be 
made  to  produce,  even  in  an  open  chimney  fireplace. 
To  recommend  the  air-tubes  to  persons  of  that  descrip- 
tion, I  would  tell  them,  that,  by  closing  up,  by  means 
of  its  register,  the  lower  branch  of  communication  (that 
which  ends  just  under  the  grate)  and  setting  that  situ- 
ated near  the  top  of  the  room  wide  open,  they  may  in- 
dulge themselves  with  having  a  very  large  fire  in  the 
room  with  little  heat,  and  this  with  much  less  inconven- 
ience from  currents  of  cold  air  from  the  doors  and  win- 
dows than  they  now  experience. 

It  is  easy  to  perceive  that  by  a  proper  use  of  the  two 
registers,  together  with  a  judicious  management  of  the 
fire,  the  air  in  the  room  may  either  be  made  hotter  or 
colder,  or  may  be  kept  at  any  given  temperature,  or  the 
room  may  be  most  effectually  ventilated ;  and  that  this 
change  of  air  may  be  effected  either  gradually  or  more 
suddenly.  And  here  it  may  perhaps  be  the  proper  place 
to  observe,  that  in  all  our  reasonings  and  speculations 
relative  to  the  heating  of  rooms  by  means  of  open  chim- 


570  Of  Chimney  Fireplaces. 

ney  fires,  we  must  never  forget  that  it  is  the  room  that 
heats  the  air •,  and  not  the  air  that  heats  the  room. 

The  rays  that  are  sent  off  from  the  burning  fuel  gen- 
erate heat  only  when  and  where  they  are  stopped  or 
absorbed;  consequently  they  generate  no  heat  in  the  air 
in  the  room  in  passing  through  it,  because  they  pass 
through  if,  and  are  not  stopped  by  it,  but,  striking  against 
the  walls  of  the  room,  or  against  any  solid  body  in  the 
room,  these  rays  are  there  stopped  and  absorbed,  and  it  is 
there  that  the  heat  found  in  the  room  is  generated.  The 
air  in  the  room  is  afterwards  heated  by  coming  into  con- 
tact with  these  solid  bodies.  Many  capital  mistakes  have 
arisen  from  inattention  to  this  most  important  fact. 

It  is  really  astonishing  how  little  attention  is  paid  to 
events  which  happen  frequently,  however  interesting 
they  may  be  as  objects  of  curious  investigation,  or 
however  they  may  be  connected  with  the  comforts  and 
enjoyments  of  life.  Things  near  us,  and  which  are 
familiar  to  us,  are  seldom  objects  of  our  meditations. 
How  few  persons  are  there  who  ever  took  the  trouble  to 
bestow  a  thought  on  the  subject  in  question,  though  it 
is,  in  the  highest  degree,  curious  and  interesting ! 

[This  paper  is  printed  from  the  English  edition  of  Rumford's 
Essays,  Vol.  III.,  pp.  387  —  400.] 


END   OF   VOL.   II. 


Cambridge :  Electrotyped  and  Printed  by  Welch,  Bigelow,  &  Co. 


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